Characteristics of the Study Sample
Overall, 2907 women were included in the study. Most of them were aged 20-30 years (59.2%), delivered through the vagina (79.8%) and were housewives (70.8%) (Table 1). For 30.6% of the women, the current pregnancy was their first and more than half (55.2%) of them delivered after 40 weeks of gestation. A little over half of all the children delivered were males (51.4%).
Overall, a higher proportion of those who attended 1-4 ANC visits (57.2%) and those who attended more than four ANC visits (62.7%) were aged 20-30 years (Table 1). Adolescent mothers attended the least number of 1-4 (21.3%) and more than 4 (12.2%) antenatal visits during the period. However, of the 149 mothers who never attended any ANC visits during pregnancy, only 20.1% of them were adolescents. A higher proportion of those who attended more than 4 ANC visits were housewives (66.8%) and 55.5% of them delivered after 40 weeks gestation and 76.6% had a vaginal delivery.
Table 1 Characteristics of the Study Sample
Characteristics
|
Antenatal visits
|
All women in the sample (n=2907)
|
Chi-squared P-value
|
None (n=149)
|
1-4 (n=1547)
|
>4 (n=1211)
|
Mothers age (in years)
|
|
|
|
|
|
<20
|
30(20.1)
|
329(21.3)
|
148(12.2)
|
507(17.5)
|
<0.001
|
20-30
|
76(51.0)
|
883(57.2)
|
759(62.7)
|
1719(59.2)
|
|
>30
|
43(28.9)
|
332(21.5)
|
303(25.1)
|
678(23.3)
|
|
Occupation
|
|
|
|
|
|
Other
|
46(30.9)
|
394(25.7)
|
405(33.6)
|
845(29.2)
|
<0.001
|
House wife
|
103(69.1)
|
1141(74.3)
|
800(66.4)
|
2045(70.8)
|
|
Number of pregnancies
|
|
|
|
|
|
1
|
45(30.2)
|
507(32.8)
|
337(27.8)
|
889(30.6)
|
0.003
|
2
|
23(15.4)
|
255(16.5)
|
257(21.2)
|
536(18.4)
|
|
3
|
19(12.8)
|
234(15.1)
|
202(16.7)
|
455(15.7)
|
|
4
|
21(12.1)
|
187(12.1)
|
170(14.0)
|
378(13.0)
|
|
5
|
13(8.7)
|
159(10.3)
|
111(9.2)
|
283(9.7)
|
|
6+
|
28(18.8)
|
204(13.2)
|
134(11.1)
|
366(12.6)
|
|
Gestational age in weeks
|
|
|
|
|
|
<31 weeks
|
6(4.1)
|
28(1.9)
|
6(0.5)
|
40(1.4)
|
<0.001
|
31-36 weeks
|
25(16.9)
|
176(11.7)
|
110(9.4)
|
311(11.0)
|
|
37-40 weeks
|
26(17.5)
|
484(32.1)
|
407(34.6)
|
917(32.4)
|
|
>40 weeks
|
91(61.5)
|
818(54.3)
|
652(55.5)
|
1562(55.2)
|
|
Sex of child
|
|
|
|
|
|
Female
|
67(45.9)
|
742(48.2)
|
598(49.5)
|
1408(48.6)
|
0.633
|
Male
|
79(54.1)
|
799(51.8)
|
611(50.5)
|
1489(51.4)
|
|
Type of delivery
|
|
|
|
|
|
Vaginal Delivery
|
100(69.9)
|
1252(83.2)
|
906(76.6)
|
2259(79.8)
|
<0.001
|
Caesarean section
|
43(30.1)
|
253(16.8)
|
277(23.4)
|
573(20.2)
|
|
Prevalence of adverse pregnancy outcomes
Of the four adverse pregnancy outcomes assessed in this study, preterm birth had the highest prevalence of 12.4% (Table 2). Low birth weight was prevalent in 9.3% of the children born during the period. Of the 2907 mothers, 4.8% delivered babies that were small for their gestational age and 2% had a stillbirth.
We found evidence for an inverse trend in the chi-squared association between ANC visits and the prevalence of adverse pregnancy outcomes (Table 2). An increase in the number of ANC visits was associated with a decrease in the number of adverse pregnancy outcomes. For instance, about 21% of mothers who never attended any ANC visits, 13.6% of those who attended 1-4 visits and 10% of those who attended more than four visits had a preterm birth, respectively (Ptrend<0.001, Table 2). Likewise, small-for-gestational-age was prevalent in 6.8% of mothers who never attended any ANC visits, 5.6% in those who made 1-4 visits, and 3.4% in those who made more than four visits. As shown in Table 2, similar trends were observed for low birth weight (Ptrend<0.001) and stillbirth (Ptrend<0.003).
Figure 1 presents the four adverse pregnancy outcomes by mothers’ age. It shows that adolescent mothers had the highest prevalence of preterm birth (12.9%), low birth weight (12.1), and small-for-gestational-age (6.4%). For stillbirth, the highest proportion was observed among mothers aged 20-30years (2.2%).
Table 2 Prevalence of adverse pregnancy outcomes
Adverse birth outcomes
|
Antenatal visits
|
All women in the sample (n=2907)
|
Chi-squared P-value for trend
|
None (n=149)
|
1-4 (n=1547)
|
>4 (n=1211)
|
Preterm birth
|
|
|
|
|
|
No
|
117(79.1)
|
1302(86.6)
|
1059(90.1)
|
2479(87.6)
|
<0.001
|
Yes
|
31(20.9)
|
204(13.6)
|
116(9.9)
|
351(12.4)
|
|
Low birth weight
|
|
|
|
|
|
No
|
128(87.7)
|
1360(88.3)
|
1137(94.0)
|
2626(90.7)
|
<0.001
|
Yes
|
18(12.3)
|
180(11.7)
|
72(6.0)
|
270(9.3)
|
|
Small-for-gestational-age
|
|
|
|
|
|
No
|
138(93.2)
|
1421(94.4)
|
1135(96.6)
|
2694(95.2)
|
0.004
|
Yes
|
10(6.8)
|
85(5.6)
|
40(3.4)
|
135(4.8)
|
|
Stillbirth
|
|
|
|
|
|
No
|
138(92.6)
|
1520(98.3)
|
1192(98.4)
|
2851(98.0)
|
0.003
|
Yes
|
11(7.4)
|
27(1.8)
|
19(1.6)
|
57(2.0)
|
|
Association of number of antenatal care visits and adverse pregnancy outcomes
There was evidence for an association between ANC visits and preterm birth in the unadjusted analysis (p<0.001). After adjusting for mothers age, the number of pregnancies, type of delivery, sex of a child, and mothers’ occupation the strength of the evidence reduced (p=0.041). Overall, mothers who attended any number of ANC visits had lower odds of preterm birth compared to those who did not attend any ANC visit (Table 3). However, the protective effect of ANC visits on preterm birth varied with the number of visits attended. For instance, compared to mothers who did not attend any ANC visit, those who attended only 1 visit were 10% less likely to have preterm birth (OR 0.90, 95%CI 0.48-1.68), those who attend 2 ANC visits were 13% less likely to have preterm birth (OR 0.87, 95%CI 0.52-1.44), while those who attended 5 and 6 ANC visits were 55% (OR 0.45, 95%CI 0.27-0.75) and 62% (OR 0.38, 95%CI 0.22-0.65) less likely to have preterm birth in the adjusted analysis, respectively.
To determine whether the association between ANC visits and preterm birth differed by mothers age, we assessed for interaction between ANC visits and mothers age (Table 5). There was good evidence that the data were consistent with an interaction between ANC visits and mothers age(p=0.035). Among mothers who did not attend any ANC visits, the odds of preterm birth were 53% and 45% less likely in adolescent mothers (OR 0.47, 95%CI 0.14-1.56) and older mothers (OR 0.55, 95%CI 0.20-1.56) compared to those aged 20-30years, respectively. Among mothers who attended more than four ANC visits, the odds of preterm birth were nearly 2 times and 1.2 times more likely in adolescent mothers (OR 1.78, 95%CI 1.03-3.05) and older mothers (OR 1.16, 95%CI 0.71-1.92) compared to those aged 20-30years.
In both the unadjusted (p<0.001) and adjusted (p<0.001) analysis, ANC visits were associated with low birth weight. After adjusting for mothers age, gestational age, the number of pregnancies, type of delivery, sex of a child, and mothers’ occupation there was an increase in all the odds ratios, except for the odds ratio for seven or more visits (Table 4). Gestational age, number of pregnancies, and mother’s occupation caused a substantial change in the odds ratios when they were introduced into the model; however, mothers age did not produce a considerable change. Furthermore, in the adjusted analysis, there was evidence for a linear trend in the effect of ANC visits on low birth weight (Ptrend<0.001). An increase in the number of ANC visits was associated with decreased odds of low birth weight. For example, those who attended only 1 ANC visit had double the odds of low birth weight (OR 1.82, 95%CI 0.87-3.78), 2 and 3 visits were associated with 1.4 (95%CI 0.72-2.61) and 1.1 (95%CI 0.56-1.97) times higher odds of low birth weight, whiles 4 and 5 visits were associated with 22% (OR 0.78, 95%CI 0.42-1.46) and 43% (OR 0.57, 95%CI 0.29-1.10) decreased odds of low birth weight compared to mothers who never attended any ANC visits.
Further analysis revealed that there was strong evidence for an interaction between ANC visits and mothers age (p<0.001), indicating that the effect of ANC visits on low birth weight differed depending on the age of the mother (Table 5). Among mothers who never attended any ANC visits, the odds of low birth weight were 1.3 times and 4.5 times more likely in adolescent mothers (OR 1.34, 95%CI 0.29-6.23) and mothers older than 30 years (OR 4.49, 95%CI 1.31-15.34) compared to those aged 20-30years, respectively. However, among mothers who attended more than four ANC visits, the odds of low birth weight were 1.2 times more likely in adolescent mothers (OR 1.20, 95%CI 0.61-2.34) and 43% less likely in mothers older than 30years (OR 0.57, 95%CI 0.26-1.27) compared to those aged 20-30years.
There was good evidence for an association between ANC visits and small-for-gestational-age in the unadjusted (P=0.016) and adjusted analysis (P=0.021). When we adjusted for mothers age, the number of pregnancies, type of delivery, sex of a child, and mothers’ occupation, the odds of small-for-gestational-age was 1.6 times more likely and 2% less likely in mothers who attended only one ANC visit (95%CI 0.66-3.97) and those who attended two ANC visits (OR 0.98, 95%CI 0.43-2.23) compared to those who did not attend any ANC visits, respectively (Table 4). While mothers who attended six ANC visits (OR 0.48, 95%CI 0.20-1.17) and those who attended seven or more visits (OR 0.46, 95%CI 0.18-1.15) were 52% and 54% less likely to have delivered small-for-gestational-age babies compared to those who did not attend any ANC visit in the adjusted analysis, respectively (Table 4).
We found evidence for an association between ANC visits and stillbirth in the unadjusted (P<0.001) and adjusted analysis (P<0.001). Overall, the adjusted analysis showed that mothers who attended any number of ANC visits were less likely to experience stillbirth compared to those who did not attend any ANC visit (Table 4). For instance, mothers who attended only 1 ANC visit (OR 0.62, 95%CI 0.19-2.07) and those who attended seven or more visits (OR 0.25, 95%CI 0.07-0.86) were 38% and 75% less likely to have experienced stillbirth compared to those who never attended any ANC visits, respectively.
Table 3 Unadjusted odds ratios and 95% confidence intervals of the association between antenatal care attendance and adverse pregnancy outcomes
Antenatal visits
|
Preterm birth
|
Low birth weight
|
Small-for-gestational age
|
Stillbirth
|
Number of antenatal visits
|
P<0.001
|
P<0.001
|
P=0.016
|
p<0.001
|
0
|
1
|
1
|
1
|
1
|
1
|
0.81(0.44-1.50)
|
1.78(0.91-3.46)
|
1.69(0.71-4.01)
|
0.55(0.18-1.62)
|
2
|
0.83(0.51-1.35)
|
1.27(0.71-2.27)
|
1.00(0.46-2.17)
|
0.44(0.19-1.04)
|
3
|
0.47(0.29-0.77)
|
0.92(0.52-1.62)
|
0.80(0.37-1.70)
|
0.14(0.05-0.40)
|
4
|
0.53(0.33-0.84)
|
0.66(0.38-1.17)
|
0.61(0.29-1.29)
|
0.12(0.04-0.33)
|
5
|
0.45(0.27-0.73)
|
0.53(0.29-0.96)
|
0.48(0.22-1.08)
|
0.30(0.13-0.69)
|
6
|
0.35(0.20-0.59)
|
0.35(0.18-0.70)
|
0.46(0.20-1.10)
|
0.10(0.03-0.36)
|
7+
|
0.45(0.26-0.76)
|
0.44(0.22-0.88)
|
0.52(0.22-1.25)
|
0.17(0.05-0.53)
|
Table 4 Adjusted odds ratios and 95% confidence intervals of the association between antenatal care attendance and adverse pregnancy outcomes
Antenatal visits
|
Preterm birtha
|
Low birth weightb
|
Small-for-gestational agec
|
Stillbirthd
|
Number of antenatal visits
|
P=0.041
|
P<0.001
|
P=0.021
|
P<0.001
|
0
|
1
|
1
|
1
|
1
|
1
|
0.90(0.48-1.68)
|
1.82(0.87-3.78)
|
1.62(0.66-3.97)
|
0.62(0.19-2.07)
|
2
|
0.87(0.52-1.44)
|
1.37(0.72-2.61)
|
0.98(0.43-2.23)
|
0.44(0.16-1.22)
|
3
|
0.50(0.30-0.83)
|
1.05(0.56-1.97)
|
0.81(0.37-1.80)
|
0.18(0.06-057)
|
4
|
0.56(0.35-0.91)
|
0.78(0.42-1.46)
|
0.65(0.29-1.42)
|
0.18(0.06-0.53)
|
5
|
0.45(0.27-0.75)
|
0.57(0.29-1.10)
|
0.45(0.19-1.06)
|
0.41(0.16-1.04)
|
6
|
0.38(0.22-0.65)
|
0.46(0.22-0.95)
|
0.48(0.20-1.17)
|
0.16(0.04-0.61)
|
7+
|
0.47(0.27-0.81)
|
0.44(0.21-0.93)
|
0.46(0.18-1.15)
|
0.25(0.07-0.86)
|
a adjusted for mothers age, number of pregnancies, type of delivery, sex of child, and mothers occupation
b adjusted for mothers age, gestational age, the number of pregnancies, type of delivery, sex of a child, and mothers’ occupation.
c adjusted for mothers age, the number of pregnancies, type of delivery, sex of a child, and mothers occupation.
d adjusted for mothers age, gestational age, the number of pregnancies, type of delivery, sex of a child, and mothers’ occupation.
Table 5 Adjusted odds ratios and 95% confidence intervals of the interaction between antenatal care attendance mothers age on adverse pregnancy outcomes
Antenatal visits
|
Preterm birtha
|
Low birth weightb
|
|
<20years
|
20-30years
|
>30years
|
<20years
|
20-30years
|
>30years
|
Number of antenatal visits
|
P=0.035
|
P<0.001
|
None
|
0.47(0.14-1.56)
|
1
|
0.55(0.20-1.56)
|
1.34(0.29-6.23)
|
1
|
4.49(1.31-15.34)
|
1-4 antenatal visits
|
0.75(0.49-1.14)
|
1
|
1.16(0.76-1.76)
|
1.06(0.70-1.62)
|
1
|
1.20(0.72-1.99)
|
>4 antenatal visits
|
1.78(1.03-3.05)
|
1
|
1.16(0.71-1.92)
|
1.20(0.61-2.34)
|
1
|
0.57(0.26-1.27)
|
a adjusted for mothers age, number of pregnancies, type of delivery, sex of child, and mothers occupation
b adjusted for mothers age, gestational age, the number of pregnancies, type of delivery, sex of a child, and mothers’ occupation.