Does antimicrobial use during pregnancy impact excess weight in early childhood? Findings from the 2015 Pelotas (Brazil) Birth Cohort Study

doi:10.21203/rs.3.rs-2082216/v1

Background: Studies have suggested that prenatal exposure to antimicrobials might be associated with obesity during childhood.

Objective: This study aimed to investigate the association between the use of antimicrobials during pregnancy and excess weight in children at ages three, 12, 24 and 48 months.

Methods: Data of participants from the 2015 Pelotas (Brazil) Birth Cohort study were analyzed (N=4,275). The use of antimicrobials during pregnancy was assessed using standardized questionnaires and excess weight was defined as BMI for age in z-score ≥ 1.

Results: Over 43% of women used at least one antimicrobial during pregnancy. The proportion of children with excess weight increased from 17.6% (95%CI 16.5; 18.8) at age 3mo to 43.8% (95%CI 42.2; 45.4) at age 48mo. Overall, most associations investigated between the use of antimicrobials during pregnancy and excess weight in children were null. The use of antimicrobials during the second trimester of pregnancy was associated with lower BMI-for-age at three months. On average, children whose mothers used antimicrobials in one trimester of pregnancy had a BMI-for-age at 12mo 0.11 z-score (95%CI 0.01; 0.20) higher than those from mothers who did not use antimicrobials. An increased risk in excess weight at 48mo [RR= 1.13 (95%CI 1.04; 1.23)] was observed among children whose mothers’ used antimicrobials in the first trimester of pregnancy.

Conclusion: Given that most of the associations investigated had either null results or a small magnitude of association, this study does not support previous findings that the use of antimicrobial during pregnancy impacts excess weight in early childhood.

pregnancy

childhood

prenatal

antimicrobial

overweight

obesity

cohort study

Adverse factors acting in the embryonic, fetal and early life period can result in adaptations in human development^1,2. These adaptations occur due to a biological programming process that produces structural, physiological and metabolic changes, which influence the occurrence of diseases across the lifespan ^1,2.

Studies have suggested that prenatal exposure to antimicrobials might be associated with the development of overweight and obesity during childhood^3,4,5, although it is still unclear whether the association of maternal antimicrobial use during pregnancy with overweight and obesity during childhood is causal. Pathophysiological mechanisms may explain this relationship. For example, the interference in the mother's microbiome caused by the use of antimicrobials during pregnancy, which plays an important role in the fetal placental circulation^6,7 may alters colonization and maturation of the infant intestinal microbiome by increasing susceptibility to obesity⁸.

Observational studies about the association between the use of antimicrobials during pregnancy and overweight and obesity in children have shown conflicting findings. In the US, participants of a cohort with 436 children who were exposed to antimicrobials during the second or third trimester of pregnancy had 84% higher risk of obesity than those unexposed⁸. Furthermore, a study conducted in China identified that the use of antibiotics during pregnancy was positively associated with the risk of obesity at five years of age. Conversely, in a cohort of 43,435 Danish children, prenatal exposure to small-spectrum antimicrobials was not associated with overweight at ages 7 and 11⁴. Also, in a cohort of 53,320 children, the use of antibiotics during pregnancy was not associated with BMI-z in childhood at five years of age⁹.

Although prospective observational studies provide important insights, the relationships between the use of antimicrobials during pregnancy and the development of excess weight in early childhood are still poorly understood. In addition, the relationships observed in population-based studies are susceptible to bias due to residual or unmeasured contextual confounding factors¹⁰. Moreover, to date, most studies that investigated the association between the use of antimicrobials during pregnancy and early childhood excess weight lack information about the time of use, type of spectrum, the class of the antimicrobial, and critical confounding variables as maternal obesity and gestational diabetes¹¹.

Therefore, the aim of this study was to investigate the association between the use of antimicrobials during pregnancy and excess weight in Brazilian children at three, 12, 24 and 48 months of age.

Population and sample

This study used data from the 2015 Pelotas (Brazil) Birth Cohort study. This population-based cohort enrolled 99% of children born in all maternity hospitals in Pelotas, a city located in southern Brazil with approximately 350,000 inhabitants, whose mothers lived in the urban area of the municipality or in Jardim América in 2015 (n = 4219 mothers, 4275 children). An antenatal study was conducted with 73.8% of women whose children were enrolled in the cohort (n = 3155). For this, all 123 health units and private clinics that provided antenatal care in the city were visited or contacted weekly between May 2014 and December 2015 to identify pregnant women who were expected to deliver their babies between January 1 and December 31, 2015.

Mothers and children were invited to further data collections when infants were three (97.2%), 12 (95.4%), 24 (95.4%) and 48 months old (95.4%). Domiciliary interviews were conducted at ages 3 and 12 months. In contrast, at 24 and 48 months, the follow-up assessments were conducted in a research clinic in the Center for Epidemiological Research of the Federal University of Pelotas. Of the 4,275 children born in 2015 and whose mothers provided information about the use of medicines during pregnancy, 4,056, 3,948, 3,718 and 3,757 had anthropometric data when they were aged three, 12, 24 and 48 months, respectively. Data collection and measurements were standardized and collected by trained research assistants through RedCap¹². In all interviews, participants provided written informed consent. The 2015 Pelotas (Brazil) Cohort Study was approved by the School of Physical Education Ethics Committee from the Federal University of Pelotas (protocol number 26746414.5.0000.5313). Further details about the study design and protocols have been published previously¹³.

Use of antimicrobials during pregnancy

Information about the use of antimicrobials during pregnancy was collected using standardized questionnaires during the antenatal and perinatal assessments using the following questions: "Did you use any medication during pregnancy?"; "What are the names of the medicines that you used during pregnancy?"¹⁴. Subsequently, the International Anatomical Therapeutical Chemical (ATC) classification of the World Health Organization¹⁵ was used to classify the drugs by therapeutic groups up to the fifth level. For this study, the use of medicines in the 'group J', which are anti-infectious for systemic use, were considered.

The following binary (yes/no) variables regarding the use of antimicrobials during pregnancy were investigated: a) Use of at least one antimicrobial during pregnancy; b) use of antimicrobial during the 1st trimester of pregnancy; c) use of antimicrobial during the 2nd trimester of pregnancy; d) use of antimicrobial during the 3rd trimester of pregnancy. Additionally, the number of trimesters of pregnancy in which antimicrobials were used (none; one; two or three), use of at least one low-spectrum antimicrobial during pregnancy (yes/no), and the use of at least one broad-spectrum antimicrobial (yes/no) were analyzed.

Anthropometric assessment

At ages three, 12, 24 and 48 months, children had their weight (g) and length/height (cm) measured by trained research assistants using standardized protocols. Weight was measured using a portable electronic scale (capacity of up to 50 kg and accuracy of 10g) at three months. For measurement of weight at 12 and 24 months, children were weighted on their mothers' laps using SECA 803 scales (SECA, Germany) with 100 g precision; child's weight was obtained as the difference between total weight (mother and children) and the weight of the mother. In all assessments, children were naked and mothers were wearing light clothes when they were weighted. At age 48 months, a portable digital scale of the Tanita® with a maximum capacity of 150 Kg and accuracy of 100g was used. Child length at three and 12 months was measured using a portable anthropometer of the SANNY® model ES2000 with an amplitude of 20 to 105 cm and precision of 0.5 cm. At 24 months, a fixed Harpenden® with a range of 30 to 110 cm and precision of 0.1 cm was used, whereas a fixed Harpenden® with maximum height of 2.06 m and accuracy of 1 mm was used when children were aged 48 months. At 24 and 48 months, 90% of measurements were performed in a research clinic in the Center for Epidemiological Research. In the remaining 10% of participants, when measurements had to be performed at home, validated portable anthropometers and stadiometers were used ¹⁶.

In each follow-up assessment, body mass index-for-age in z-scores was calculated according to the World Health Organization (WHO) Child Growth Standards¹⁷. WHO ANTHRO macros for STATA were used according to the methodology recommended by the WHO.¹⁸ For this study, excess weight was defined as BMI-for-age ≥ 1 standard deviation¹⁷.

Covariates

The following confounding variables were measured using standardized questionnaires and included in the analyses: number of pregnancies (one/ two/three or more); number of prenatal consultations (< 6/7 or more); maternal smoking during pregnancy (no/yes); maternal consumption of alcohol during pregnancy (no/yes), hypertension (no/yes) and self-reported diabetes mellitus (no/yes) during pregnancy, maternal skin color (white/black/brown); maternal age (13–19 / 20–24 / 25–29 / 30–34 / 35 or more); maternal education (0–4 / 5–8 / 9–11 / 12 years or more); maternal marital status (with partner / no partner) and pre-gestational maternal BMI (≤ 24.9 / 25 to < 30.0 / ≥ 30.0 kg/m²).

Statistical analysis

Descriptive statistics were used to describe and compare sociodemographic characteristics of the original cohort with the analytical sample of each follow-up assessment. Absolute and relative frequencies were used to describe the use of antimicrobials during pregnancy. Mean and standard deviation of BMI-for-age in z-score, and prevalence of excess weight in each age were described according to the use of antimicrobials during pregnancy (as previously described).

The associations of each variable used to describe the use of antimicrobials during pregnancy with BMI-for-age and excess weight at each age were examined using, respectively, linear regression and Poisson regression models with adjustment for robust variance. Crude and adjusted analyses were conducted. The potential confounders were considered, but only those associated with the dependent variable (p-value of < 0.20) were included in the final model. Given the number of comparisons and the potential for type 1 error, interpretation of findings was based on the magnitude of associations (regression coefficients) and overlap of 95% confidence intervals (CI). All analyses were performed in the Stata®15.0.

Sociodemographic and health characteristics of the participants in the original cohort and each follow-up are presented in Table 1. There were no marked differences between the original cohort and those who participated in the follow-up assessments. At the time of delivery, most women were aged 20–34 years, had white skin color, had a partner, had 9–11 years of formal education, and nearly 20% of women were obese before pregnancy. Most women reported seven or more prenatal consultations (76.1%), 44.5% had only one child, 16.5% reported smoking during pregnancy, and 7.4% consumed alcohol. One in four women reported hypertension during pregnancy, and 8.6% had gestational diabetes (Table 1).

Table 1: Sample characteristics of the 2015 Pelotas (Brazil) Birth Cohort Study.

	Original Cohort (n= 4,275) n (%)	3 months (n= 4,056)* n (%)	12 months (n= 3,948)* n (%)	24 months (n= 3,718)* n (%)	48 months (n= 3,757)* n (%)
Maternal age (in years)
13-19	623 (14.6)	594 (14.7)	577 (14.6)	546 (14.7)	546 (14.5)
20-24	1,008 (23.6)	959 (23.6)	932 (23.6)	866 (23.3)	903 (24.0)
25-29	1,006 (23.5)	961 (23.7)	930 (23.6)	873 (23.5)	879 (23.4)
30-34	1,004 (23.5)	953 (23.5)	931 (23.6)	888 (23.9)	879 (23.4)
35+	633 (14.8)	588 (14.5)	578 (14.6)	545 (14.6)	550 (14.7)
Maternal skin color
White	3,071 (71.9)	2,912 (71.9)	2,827 (71.7)	2,653 (71.4)	2,680 (71.4)
Brown	561 (13.1)	608 (15.0)	603 (15.3)	574 (15.5)	579 (15.4)
Black	639 (15.0)	532 (13.1)	514 (13.0)	487 (13.1)	494 (13.2)
Maternal marital status
Single mother	607 (14.2)	576 (14.2)	548 (13.9)	512 (13.8)	528 (14.1)
With partner	3,667 (85.8)	3,479 (85.8)	3,399 (86.1)	3,205 (86.2)	3,228 (85.9)
Maternal education (years)
0-4	391 (9.2)	366 (9.0)	348 (8.8)	336 (9.0)	327 (8.7)
5-8	1,095 (25.6)	1,043 (25.7)	1,013 (25.7)	970 (26.1)	981 (26.1)
9-11	1,458 (34.1)	1,397 (34.5)	1,376 (34.9)	1,288 (34.7)	1,312 (35.0)
12+	1,330 (31.1)	1.249 (30.8)	1,210 (30.6)	1,123 (30.2)	1,136 (30.2)
Pre-pregnancy BMI (kg/m²)
≤ 24.9	2,193 (53.0)	2,076 (52.8)	2,021 (52.8)	1,919 (53.1)	1,910 (52.4)
25.0 until < 30.0	1,169 (28.2)	1,108 (28.2)	1,077 (28.1)	995 (27.6)	1,037 (28.4)
≥ 30.0	779 (18.8)	750 (19.0)	733 (19.1)	696 (19.3)	699 (19.2)
Number of prenatal consultations
< 6	1,001 (23.9)	929 (23.3)	891 (23.0)	829 (22.7)	841 (22.8)
7 or more	3,185 (76.1)	3,052 (76.7)	2,988 (77.0)	2,828 (77.3)	2,852 (77.2)
Parity (number of previous children)
1	1,900 (44.5)	1,805 (44.5)	1,765 (44.7)	1,655 (44.5)	1,665 (44.3)
2	1,285 (30.0)	1,228 (30.3)	1,200 (30.4)	1,108 (29.8)	1,146 (30.5)
3 or more	1,089 (25.5)	1,022 (25.2)	982 (24.9)	954 (25.7)	945 (25.2)
Pregnancy smoking
No	3,567 (83.5)	3,393 (83.7)	3,314 (84.0)	3,112 (83.8)	3,142 (83.7)
Yes	705 (16.5)	661 (16.3)	631 (16.0)	603 (16.2)	612 (16.3)
Pregnancy alcohol
No	3,957 (92.6)	3,760 (92.8)	3,657 (92.7)	3,438 (92.5)	3,472 (92.5)
Yes	315 (7.4)	294 (7.2)	288 (7.3)	277 (7.5)	282 (7.5)
Gestational arterial hypertension
No	3,183 (74.5)	3,018 (74.5)	2,934 (74.4)	2,780 (74.8)	2,804 (74.7)
Yes	1,089 (25.5)	1,035 (25.5)	1,012 (25.6)	935 (25.2)	950 (25.3)
Gestational diabetes
No	3,906 (91.4)	3,706 (91.4)	3,600 (91.2)	3,389 (91.2)	3,425 (91.2)
Yes	366 (8.6)	347 (8.6)	346 (8.8)	326 (8.8)	329 (8.8)

*Analytical sample

The prevalence of total antimicrobial use during pregnancy was 43.4% (95%CI 41.9; 44.9). The proportion of women who used antimicrobials in each trimester was approximately 20% (18%, 21%, and 21% in the first, second and third trimester, respectively); 30.4% of women reported use in only one trimester, and 13.0% reported use of antimicrobials in two or three trimesters of pregnancy. One-third of the women used antimicrobials classified as a small spectrum, and only 2.9% used antimicrobials classified as broad-spectrum (Table 2). The most used antimicrobials were cephalexin (23.6%), amoxicillin (15.8%), nitrofurantoin (15.6%) and ampicillin (5.9%) (Supplementary Table).

Table 2

Use of antimicrobials and nutritional indicators at 3, 12, 24 and 48 months. 2015 Pelotas (Brazil) Birth Cohort Study.
	Use of antimicrobials	Nutritional status (z-score)				Excess of weight*
	N (%)	Mean (SD) 3m	Mean (SD) 12 m	Mean (SD) 24 m	Mean (SD) 48 m	% 3 m	% 12 m	% 24 m	% 48 m
Total use
No	2,383 (56.6)	0.06 (0.03)	0.65 (0.03)	0.56 (0.03)	1.11 (0.05)	17.8	38.5	32.4	43.7
Yes	1,827 (43.4)	0.05 (0.03)	0.72 (0.03)	0.56 (0.03)	1.06 (0.05)	17.5	40.6	32.8	44.3
1st trimester
No	3,451 (82.0)	0.06 (0.02)	0.67 (0.02)	0.55 (0.02)	1.08 (0.04)	17.6	38.7	32.1	42.8
Yes	759 (18.0)	0.06 (0.04)	0.73 (0.05)	0.59 (0.04)	1.13 (0.08)	18.2	42.6	34.6	49.1
2nd trimester
No	3,306 (78.5)	0.08 (0.02)	0.69 (0.02)	0.57 (0.02)	1.09 (0.04)	18.1	39.8	32.4	44.0
Yes	904 (21.5)	-0.02 (0.04)	0.64 (0.04)	0.53 (0.04)	1.09 (0.09)	16.2	38.1	32.9	43.8
3rd trimester
No	3,311 (78.7)	0.05 (0.02)	0.67 (0.02)	0.55 (0.02)	1.11 (0.04)	17.5	39.4	32.5	44.2
Yes	899 (21.3)	0.09 (0.04)	0.73 (0.05)	0.59 (0.04)	1.04 (0.06)	18.4	39.7	32.5	43.4
Pregnancy
No	2,383 (56.6)	0.07 (0.03)	0.64 (0.03)	0.56 (0.03)	1.11 (0.05)	17.8	38.5	32.4	43.7
1	2,383 (30.4)	0.05 (0.03)	0.76 (0.04)	0.57 (0.03)	1.08 (0.06)	17.5	41.9	33.0	44.0
2+	545 (13.0)	0.05 (0.05)	0.63 (0.05)	0.54 (0.05)	1.01 (0.07)	17.5	37.8	32.1	45.2
Small spectrum
No	2,932 (68.8)	0.06 (0.02)	0.67 (0.03)	0.57 (0.02)	1.12 (0.05)	17.5	39.1	32.8	44.1
Yes	1,327 (31.2)	0.06 (0.03)	0.69 (0.04)	0.53 (0.03)	1.03 (0.06)	18.2	40.3	32.0	43.7
Broad-spectrum
No	4,137 (97.1)	0.06 (0.02)	0.68 (0.02)	0.56 (0.02)	1.09 (0.04)	17.6	39.4	32.3	43.7
Yes	122 (2.9)	0.10 (0.09)	0.72 (0.11)	0.71 (0.13)	1.10 (0.16)	18.6	41.7	40.2	51.8
Excess of weight: z-score ≥ 1 standard deviation (SDs) up to ≥ 2 SDs.

The mean BMI-for-age was 0.06 (SD = 0.02), 0.68 (SD = 0.02), 0.56 kg/m² (SD = 0.02) and 1.08 (SD = 0.04), at three, 12, 24 and 48 months, respectively. The prevalence of excess weight was 17.6% (95%CI 16.5; 18.8) at three months, 39.4% (95%CI 37.9; 40.9) at 12, 32.4% (95%CI 30.9; 33.9) at 24 and 43.8% (95%CI 42.2; 45.4) at 48 months. Overall, not marked variations in the distribution of BMI-for-age and excess weigh at each age according to use of antimicrobials during pregnancy was observed (Table 2)

Crude and adjusted associations of use of antimicrobials during pregnancy with BMI-for-age and excess weight at three, 12, 24 and 48 months are presented in Tables 3 and 4, respectively. Overall, the use of antimicrobials during pregnancy were not associated with either BMI-for-age or excess weight, regardless the age. Of the 56 associations investigated, statistically significant findings (based on 95%CI) were only observed on three occasions, although with a small magnitude of associations. Children from mothers who used antimicrobials during the second trimester had on average 0.12 lower z-score of BMI-for-age at age 3 months than children whose mother did not use antimicrobials in the second trimester. At age 12 months, the z-score of BMI-for-age was slightly higher (β: 0.11; 95%CI: 0.01; 0.20) in children whose mothers used one antimicrobial during pregnancy than in those children of mothers who did not use antimicrobials. Children aged 48 months, whose mothers used antimicrobials in the first trimester of pregnancy, had a higher risk of excess weight than those of mothers who did not use antimicrobials in the first trimester [RR = 1.13 (95%CI 1.04; 1.23)] (Table 4).

Table 3

Association between use of antimicrobials during pregnancy and child nutritional status at 3, 12, 24 and 48 months. 2015 Pelotas (Brazil) Birth Cohort Study.
	3 months		12 months		24 months		48 months
	β crude (95%CI)	β adjusted (95%CI)	β crude (95%CI)	β adjusted (95%CI)	β crude (95%CI)	β adjusted (95%CI)	β crude (95%CI)	β adjusted (95%CI)
Total use
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
Yes	-0.02 (-0.08; 0.05)	-0.03 (-0.10; 0.03)	0.08 (-0.008; 0.16)	0.06 (-0.02; 0.15)	-0.006 (-0.08; 0.07)	-0.02 (-0.10; 0.05)	-0.05 (-0.19; 0.09)	-0.06 (-0.20; 0.09)
1st trimester
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
Yes	-0.002 (-0.09; 0.08)	-0.005 (-0.09; 0.08)	0.06 (-0.04; 0.17)	0.04 (-0.07; 0.15)	0.04 (-0.06; 0.13)	0.02 (-0.07; 0.12)	0.05 (-0.13; 0.23)	0.03 (-0.15; 0.21)
2nd trimester
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
Yes	-0.10 (-0.18; -0.02)	-0.12 (-0.20; -0.04)	-0.05 (-0.15; 0.05)	-0.06 (-0.17; 0.04)	-0.04 (-0.13; 0.47)	-0.05 (-0.14; 0.04)	0.002 (-0.17; 0.17)	0.02 (-0.15; 0.19)
3rd trimester
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
Yes	0.03 (-0.05; 0.11)	0.02 (-0.06; 0.10)	0.06 (-0.04; 0.16)	0.05 (-0.05; 0.15)	0.03 (-0.06; 0.12)	0.02 (-0.07; 0.12)	-0.07 (-0.24; 0.10)	-0.07 (-0.24; 0.09)
Pregnancy
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
1	-0.01 (-0.09; 0.06)	-0.03 (-0.11; 0.04)	0.12 (0.02; 0.21)	0.11 (0.01; 0.20)	0.004 (-0.08; 0.09)	-0.01 (-0.10; 0.07)	-0.03 (-0.19; 0.13)	0.02 (-0.18; 0.14)
2+	-0.02 (-0.12; 0.08)	-0.04 (-0.14; 0.06)	-0.02 (-0.15; 0.11)	-0.04 (-0.17; 0.09)	-0.03 (-0.14; 0.08)	-0.05 (-0.16; 0.06)	-0.10 (-0.32; 0.11)	-0.13 (-0.35; 0.08)
Small spectrum
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
Yes	-0.001 (-0.07; 0.07)	-0.03 (-0.10; 0.05)	0.01 (-0.08; 0.10)	-0.01 (-0.10; 0.08)	-0.04 (-0.12; 0.04)	-0.07 (-0.15; 0.01)	-0.09 (-0.24; 0.06)	-0.11 (-0.26; 0.05)
Broad spectrum
No	Ref	Ref	Ref	Ref	Ref	Ref	Ref	Ref
Yes	0.04 (-0.15; 0.24)	0.08 (-0.12; 0.28)	0.04 (-0.20; 0.29)	0.06 (-0.19; 0.31)	0.16 (-0.06; 0.37)	0.12 (-0.10; 0.34)	0.008 (-0.41; 0.42)	-0.15 (-0.56; 0.27)
β: regression coefficient; 95%CI: 95% confidence interval. Adjusted for maternal age, maternal skin colour, maternal marital status, maternal education, family income, maternal prepregnancy BMI, number of prenatal consultations, parity, pregnancy smoking, pregnancy alcohol, gestational hypertension and gestational diabetes.

Table 4: Association between use of antimicrobials during pregnancy and excess weight* at 3, 12, 24 and 48 months. 2015 Pelotas (Brazil) Birth Cohort Study.

	3 months		12 months		24 months		48 months
	RR _crude (95%CI)	RR _adjusted (95%CI)	RR _crude (95%CI)	RR _adjusted (95%CI)	RR _crude (95%CI)	RR _adjusted (95%CI)	RR _crude (95%CI)	RR _adjusted (95%CI)
Total use
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Yes	0.98 (0.86; 1.12)	0.97 (0.85; 1.11)	1.05 (0.98; 1.14)	1.04 (0.96; 1.13)	1.01 (0.92; 1.11)	0.98 (0.89; 1.07)	1.01 (0.94; 1.09)	1.01 (0.94; 1.08)
1^st trimester
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Yes	1.03 (0.86; 1.25)	1.04 (0.87; 1.23)	1.10 (1.00; 1.21)	1.08 (0.98; 1.19)	1.08 (0.96; 1.21)	1.05 (0.93; 1.18)	1.15 (1.05; 1.25)	1.13 (1.04; 1.23)
2^nd trimester
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Yes	0.90 (0.74; 1.08)	0.90 (0.76; 1.06)	0.96 (0.87; 1.05)	0.96 (0.87; 1.05)	1.01 (0.91; 1.13)	0.99 (0.88; 1.11)	0.99 (0.91; 1.09)	1.00 (0.92; 1.10)
3^rd trimester
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Yes	1.06 (0.89; 1.26)	1.06 (0.90; 1.25)	1.01 (0.92; 1.11)	1.00 (0.91; 1.10)	1.00 (0.89; 1.12)	0.98 (0.87; 1.10)	0.98 (0.90; 1.07)	0.98 (0.90; 1.07)
Pregnancy
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
1	0.98 (0.83 - 1.16)	0.97 (0.84; 1.13)	1.09 (1.00; 1.18)	1.07 (0.98; 1.17)	1.02 (0.92; 1.13)	0.99 (0.89; 1.10)	1.01 (0.93; 1.09)	1.01 (0.93; 1.09)
2+	0.98 (0.78 - 1.23)	0.97 (0.79; 1.20)	0.98 (0.87; 1.11)	0.97 (0.85; 1.09)	0.99 (0.86; 1.15)	0.96 (0.83; 1.11)	1.03 (0.93; 1.15)	1.03 (0.92; 1.14)
Small spectrum
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Yes	1.04 (0.90; 1.20)	1.02 (0.88; 1.18)	1.03 (0.95; 1.12)	1.01 (0.93; 1.10)	0.98 (0.88; 1.08)	0.94 (0.85; 1.05)	0.99 (0.92; 1.07)	0.98 (0.91; 1.06)
Broad-spectrum
No	1.00	1.00	1.00	1.00	1.00	1.00	1.00	1.00
Yes	1.06 (0.72; 1.55)	1.11 (0.76; 1.62)	1.06 (0.85; 1.31)	1.06 (0.85; 1.32)	1.24 (0.99; 1.57)	1.20 (0.94; 1.53)	1.18 (0.99; 1.42)	1.14 (0.94; 1.37)

RR: Relative risk; 95%CI: 95% confidence interval. Adjusted for maternal age, maternal skin colour, maternal marital status, maternal education, family income, maternal prepregnancy BMI, number of prenatal consultations, parity, pregnancy smoking, pregnancy alcohol, gestational hypertension and gestational diabetes. Excess of weight: z-score ≥ 1 standard deviation (SDs) up to ≥ 2 SDs.

It is well known that the exposure of the fetus to certain substances can affect many aspects of child development ^19,20. In this unique representative population-based cohort study conducted in a large middle-income country, we used a range of different exposure variables, a comprehensive list of potential confounders and two indicators of children nutritional status in four time points to explore the extent to which maternal use of antimicrobials during pregnancy may impact children BMI-for-age and excess weight during the first 48 months postpartum. Overall, the findings of this study suggest that antimicrobial use during pregnancy does not influence the nutritional status of children up to age 48 months.

The proportion of women who used at least one antimicrobial during pregnancy in our study (43%) was higher than the prevalence of antimicrobial use by pregnant women in large population-based studies conducted in New Zealand (35.7%)²¹ and the United States (25.2%)²². Moreover, as previously reported²³, the prevalence of antimicrobial use tends to be the lowest in the first trimester. This can be caused by the high prevalence of urinary and genital infections in the second and third trimester of pregnancy²⁴, since urinary infections are the most common infectious diseases in this period²⁵. Furthermore, early in the pregnancy, women may be more afraid to use medications due to the risk of causing adverse effects on the fetus.

Findings from previous studies that investigated the association between the use of antimicrobials during pregnancy and childhood nutrition status have shown conflicting results. Cassidy-Bushrow et al. (2018)²⁶ evaluated 24 months old infants and found no evidence of association between the use of antimicrobials during the prenatal period and the excess weight. Similar to our findings, they also found isolated positive association when they analyzed the use of antimicrobials per trimester of pregnancy, yet with a small magnitude of associations observed²⁶. Conversely, Lin et al. (2020)²⁷ have found that among 4,909 children aged one to four years, exposure to antimicrobials during pregnancy was associated with a higher risk of excess weight only in female children aged 12 months. In our study, sensitivity analyses were conducted and showed that associations observed did not vary by sex (data not shown).

Regarding the type of antimicrobial used, Cassidy-Bushrow et al. (2018)²⁶ found a significant association between the use of macrolides during pregnancy with BMI-for-age (BMI z-score 0.37; SD:0.18; p = 0.039). They found no association with other types of antimicrobials²⁶. Macrolides are broad-spectrum antibacterial. In the present study, most pregnant women used small-spectrum antimicrobials, and no association with overweight was found according to the type of antimicrobials used.

A recent systematic review of 23 studies which analyzed data from over 1.2 million participants found that prenatal antimicrobial exposure is not associated with an excess of weight or childhood obesity. However, subgroup analyses were performed in this review indicating an increased risk of excess weight when use was in the second trimester of pregnancy (RR = 1.13; IC95% CI: 1.06; 1.22; p = 0.001)²⁸. Thus, the results of this review are in accordance with the isolated findings found in our and previous studies²⁹.

A study with 10,000 school-age children in Denmark found an association between the use of antimicrobials with excess weight in school children whose birth weight was more than 3500g and whose mothers used antimicrobials during pregnancy (PR = 1.30, 95%CI 1.05;1.61)³. In that study, antimicrobial exposure in the second trimester (PR: 1.39, 95% CI: 1.11;1.73) and in the third trimester of pregnancy (PR: 1.43, 95% CI: 1.17;1.76) were associated with increased excess weight in school-age children. Furthermore, the prevalence of excess weight increased according to the number of antimicrobials prescribed to the mother (p = 0.001) but not with the type of antimicrobial³. Sensitivity analyzes in our study were conducted and did not show differential associations according to birth weight status of children (data not shown).

Among members of Kaiser Permanente Northern California cohort study³⁰, with data collected from 2007 to 2015, there was no increased risk of obesity in children whose mothers had controlled infection, either by type of antimicrobials or in terms of dose-response ratio. However, untreated maternal infection (i.e., those mothers who required an antimicrobial but did not use it) was associated with a higher risk of obesity (OR = 1.09 CI: 1.03; 1.16). These results were confirmed utilizing a sensitivity analysis among discordant siblings, i.e., pairing with children of the same mother with pregnancy without infection or using antimicrobials, which allowed additional control of unmeasured confounding factors, including genetic, intrauterine maternal and family factors.

Limitations of our study should be acknowledged. Maternal diet during pregnancy was not assessed, which can directly interact with the children's weight. However, our analyses accounted for maternal pre-pregnancy BMI as a potential confounder. Self-reported antimicrobial use may lead to misclassification of antimicrobials, as mothers may confuse the names of medications or not remember if they used antimicrobials. However, this may be more important to symptomatic or less impactful treatments in the context of pregnancy, which is not the case for the treatment of infections. The time and duration of antimicrobial use were not assessed in our study, only the frequency of use per trimester of pregnancy. However, our analyses of the number of trimesters that antimicrobials were used showed similar results to those from trimester-specific use.

Despite the controversies regarding the association between the use of antimicrobials during pregnancy and excess weight in children, the findings of our study suggest that the use of antimicrobials during pregnancy may not impact children excess weight up to 48 months postpartum.

Funding Sources: This manuscript is based on data from the 2015 Pelotas (Brazil) Birth Cohort Study, which is conducted by the Postgraduate Program in Epidemiology, Universidade Federal de Pelotas, with the collaboration of the Brazilian Public Health Association (ABRASCO). The 2015 Pelotas (Brazil) Birth Cohort is funded by the Wellcome Trust (095582). Funding for specific follow-up visits was also received from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and Fundação de Amparo a Pesquisa do Estado do Rio Grande do Sul (FAPERGS) and Children’s Pastorate sponsored follow-up at twenty-four months.

Conflict of Interest Statement: The authors have no conflicts of interest to declare.

Barker DJ. Mothers, babies, and health in later life. 2nd ed. Edinburgh: Churchill Livingstone; 1998.
Barker DJP. The developmental origins of adult disease. Eur J Epidemiol 2003; 18: 733–736.
Mor A, Antonsen S, Kahlert J, Holsteen V, Jørgensen S, Holm-Pedersen J et al. Prenatal exposure to systemic antibacterials and overweight and obesity in Danish schoolchildren: a prevalence study. Int J Obes 2015; 39: 1450–1455.
Zhuang C, Liao X, Fu M, Shi H, Lin B, Zhu C et al. Association between the use of antibiotics during pregnancy and obesity in 5-year-old children. Transl Pediatr 2021; 10: 1686–1691.
Wang B, Liu J, Zhang Y, Yan C, Wang H, Jiang F et al. Prenatal Exposure to Antibiotics and Risk of Childhood Obesity in a Multicenter Cohort Study. Am J Epidemiol 2018; 187: 2159–2167.
Pacifici GM. Placental transfer of antibiotics administered to the mother: a review. Int J Clin Pharmacol Ther 2006; 44: 57–63.
Aagaard K, Ma J, Antony KM, Ganu R, Petrosino J, Versalovic J. The placenta harbors a unique microbiome. Sci Transl Med 2014; 6: 237ra65.
Mueller NT, Bakacs E, Combellick J, Grigoryan Z, Dominguez-Bello MG. The infant microbiome development: mom matters. Trends in Molecular Medicine 2015; 21: 109–117.
Heerman WJ, Daley MF, Boone-Heinonen J, Rifas-Shiman SL, Bailey LC, Forrest CB et al. Maternal antibiotic use during pregnancy and childhood obesity at age 5 years. Int J Obes 2019; 43: 1202–1209.
Medronho R; Bloch KV; Luiz RR; Werneck GL (eds.). Epidemiologia. Atheneu, São Paulo, 2009, 2<isupvertical-align:super;>a</isupvertical-align:super;> Edição..
Milliken S, Allen RM, Lamont RF. The role of antimicrobial treatment during pregnancy on the neonatal gut microbiome and the development of atopy, asthma, allergy and obesity in childhood. Expert Opin Drug Saf 2019; 18: 173–185.
Harris PA, Taylor R, Thielke R, Payne J, Gonzalez N, Conde JG. Research electronic data capture (REDCap)--a metadata-driven methodology and workflow process for providing translational research informatics support. J Biomed Inform 2009; 42: 377–381.
Bertoldi AD, Barros FC, Hallal PRC, Mielke GI, Oliveira PD, Maia MFS, Horta BL, Gonçalves H, Barros AJD, Tovo-Rodrigues L, Murray J, Victora CG; Pelotas Cohorts Study Group. Trends and inequalities in maternal and child health in a Brazilian city: methodology and sociodemographic description of four population-based birth cohort studies, 1982–2015. Int J Epidemiol 2019 Apr 1;48(Suppl 1):i4-i15. doi: 10.1093/ije/dyy170.
Lutz BH, Miranda VIA, Silveira MPT, Dal Pizzol T da S, Mengue SS, da Silveira MF et al. Medication Use among Pregnant Women from the 2015 Pelotas (Brazil) Birth Cohort Study. Int J Environ Res Public Health 2020; <bvertical-align:super;>17</bvertical-align:super;>: E989.
World Health Organization. Collaborating Centre for Drug Statistics Methodology. Guidelines for ATC classification and DDD assignment 2014. Available on: whocc.no/atc_ddd_index/..
Flores TR, Bertoldi AD, Ricardo LI, Blumenberg C, Moreira LR, Dias M et al. Validity assessment of a portable anthropometer to measure length in 24-month children from the 2015 Pelotas Birth Cohort. Public Health Nutrition 2020; 23: 2711–2716.
World Health Organization (WHO). Multicentre Growth Reference Study Group. WHO child growth standards based on length/height, weight, and age. Acta Paediatr 2006;(S450): 76–85..
World Health Organization (WHO). Anthro for personal computers, version 2, 2007: Software for assessing growth and development of the world's children. Geneva: WHO; 2007. Available on: http://www.who.int/childgrowth/software/en/.
Knobloch J, Jungck D, Koch A. The Molecular Mechanisms of Thalidomide Teratogenicity and Implications for Modern Medicine. Curr Mol Med 2017; 17: 108–117.
Kornum JB, Nielsen RB, Pedersen L, Mortensen PB, Nørgaard M. Use of selective serotonin-reuptake inhibitors during early pregnancy and risk of congenital malformations: updated analysis. CLEP 2010; 2: 29–36.
Leong KSW, McLay J, Derraik JGB, Gibb S, Shackleton N, Taylor RW et al. Associations of Prenatal and Childhood Antibiotic Exposure With Obesity at Age 4 Years. JAMA Netw Open 2020; 3: e1919681.
Wang B, Liu J, Zhang Y, Yan C, Wang H, Jiang F et al. Prenatal Exposure to Antibiotics and Risk of Childhood Obesity in a Multicenter Cohort Study. Am J Epidemiol 2018; 187: 2159–2167.
Zhang M, Differding MK, Benjamin-Neelon SE, Østbye T, Hoyo C, Mueller NT. Association of prenatal antibiotics with measures of infant adiposity and the gut microbiome. Ann Clin Microbiol Antimicrob 2019; 18: 18.
Ipe D, Horton E, Ulett G. The Basics of Bacteriuria: Strategies of Microbes for Persistence in Urine. Front Cell Infect Microbiol 2016. doi:10.3389/fcimb.2016.00014.
Foxman B. Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. Dis Mon 2003; 49: 53–70.
Cassidy-Bushrow AE, Burmeister C, Havstad S, Levin AM, Lynch SV, Ownby DR et al. Prenatal antimicrobial use and early-childhood body mass index. Int J Obes (Lond) 2018; 42: 1–7.
Lin M, Song H, Liu W, Su W, Yan F, Huang B et al. Sex-specific associations between prenatal antibiotics exposure and offspring's body mass index. Int J Obes (Lond) 2020; 44: 2044–2051.
Wan S, Guo M, Zhang T, Chen Q, Wu M, Teng F et al. Impact of Exposure to Antibiotics During Pregnancy and Infancy on Childhood Obesity: A Systematic Review and Meta-Analysis. Obesity (Silver Spring) 2020; 28: 793–802.
Prenatal antimicrobial use and early-childhood body mass index | International Journal of Obesity. https://www.nature.com/articles/ijo2017205 (accessed 29 Sep2021).
Li D-K, Chen H, Ferber J, Odouli R. Maternal infection and antibiotic use in pregnancy and the risk of childhood obesity in offspring: a birth cohort study. Int J Obes 2020; 44: 771–780.

(Not answered)

SupplementaryTable.docx

Does antimicrobial use during pregnancy impact excess weight in early childhood? Findings from the 2015 Pelotas (Brazil) Birth Cohort Study

Status:

Version 1

Abstract

Introduction

Methods

Population and sample

Use of antimicrobials during pregnancy

Anthropometric assessment

Covariates

Statistical analysis

Results

Discussion

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1