Birthweight Percentiles for Twins Based on Sex and Chorionicity in the South of China


 Birthweight percentile chart for different gestational age was served as an essential tool in the appropriate evaluation of neonates. Such percentile chart for twins based on different chrionicity were less reported. The aim of this study was to construct up-to-data sex specific twin neonates birth weight references by gestational ages based on different chorionicity in South of China. We retrospectively analysis 3431 twins birthweight born between 25 weeks and 40 weeks gestational age based on sex and chrionicity between 2015 to 2020 in local hospital. The smoothed birthweight percentile curves were conducted through the method, Generalized Additive Models for Location Scale and Shape (GAMLSS) .The mean birth weight of monochorionic twins were significantly lower than that of dichorionic twins , and the gestational week of delivery were earlier. The calculated 50th percentile birthweight values of twin boys were higher than those for girls based on the same chorionicity, except male monochorionic twins who were born before 31 weeks gestational age. Neonates birthweight percentile chart based on sex and chrionicity provide a tool for assessing the well being of twin infants. Use twin growth charts based on chrionicity is likely to prevent the over-diagnosis of SGA in normal growth twins.


Introduction
Birthweight could further impact on physical and mental health during the later life and also can predict the health of the newborn [9]. Birthweight percentile chart was used by obstetrician and neonatologist to evaluate whether the birthweight of neonates was appropriate for gestational age or not. In 2006, World Health Organization (WHO) published percentile charts of singleton pregnancies based on multicenter studies [1]. It was reported that twin births account for 2-4% of all birth worldwide [8; 24]. The adverse outcome of twin pregnancies were extremely higher than singleton pregnancies including low birthweight.
It is important to assess whether the birthweight of neonates was appropriate for gestational age or not.
Previous studies have suggested that it may not be suitable for using singleton birthweight percentile chart to evaluate twins [8].
Birthweight percentile for twins based on sex have been published and updated in several countries and area, including Argentina [21], Australia [18], Canada [3], Germany [22], Japan [15], Norway [6], Taiwan [8] and Wuhan city in China [24]. However, the data analysis didn't based on chorionicity of twins which has been considered to be the decisive factor in the outcome of twin pregnancy.
The main goal of this study is to construct and present up-to-date sex and chorionicity speci c twins birthweight percentile chart based on data from a population of neonates born in Guangzhou, a large city located in South China. This study could used in the assessment of the growth of twins neonates in South China.

Results
The mean gestational age and neonatal birthweight were calculated according to neonatal sex, chorionicity, mode of delivery and presence of preterm birth as shown in table 1. Overall, the mean birth weight of monochorionic twins were signi cantly lower than that of dichorionic twins (t=7.57,P=0.006), and the gestational week of delivery were earlier in monochorionic twins(t=18.71,P<0.001). The mean gestational age of delivery of female twin in monochorionic ones were statistically earlier than dichorionic ones(t=6.099,P=0.014). For female twins, the mean birth weight of monochorionic ones were lower than dichorionic ones, although the difference was non-signi cant (t=2.704,P=0.100). For male twins, the mean birth weight of monochorionic ones were lower than dichorionic ones (t=5.528,P=0.019),and the gestational week of delivery were earlier in monochorionic twins(t=13.591,P<0.001).
Mean values and standard deviations for neonatal birth weight by gestational age and values estimated for the 3rd, 10th, 50th, 75th, 90th and 97th birth weight percentiles were presented by gestational age for monochorionic and dichorionic twin girls and boys in Tables 2-5.Corresponding, the smoothed reference curves were respectively shown in Fig1-4.
The obtained results con rmed the appearance of sexual dimorphism in birth weight based on different chorionicity. The calculated 50th percentile birthweight values of twin boys were higher than those for girls based on the same chorionicity. These differences were observed in all weeks of gestational age dichorionic twins. However, the calculated values of the 50th percentile for monochorionic twin boys were lower than those for girls before 31 weeks gestational age.
The median values of birth weight by gestational age (50th percentile) between singletons and twins based on different chorionicity were compared using the values from the singleton nationwide cohort in China [25] as references. (Tables 6-7) The results re ected that the50 th percentile values of singleton birthweight of boys before 27 weeks gestational age were lower than monochorionic and dichorionic twins, while the birthweight of other gestational age of singleton boys and all gestational age of singleton girls were signi cantly higher than monochorionic and dichorionic twins at the same gestational age.

Discussion
This cross-sectional study presented neonatal birthweight references of sex-speci c twin in different chorionicity between 25 and 40 weeks gestation age, based on population in Guangzhou city, China, during 2015-2019.This study is the rst to provide gestational-age-speci c weight references based on different dichorionicity for twins in the South of China.
Birth weight is an important indicator of fetal intrauterine development [12]. The use of neonatal birth weight curve to assess infants' growth is a usual practice. Pediatricians and neonatologists depend one these standards during the decides making if the observed variability of growth curve within the led of physiological variation or whether it indicates beyond the limits of normal led [11]. Besides, obstetricians also share the opinion that birthweight percentile charts special for twins deserve emphasis [11].
Percentile charts for fetal weight in given gestational weeks are used as one of the parameters helpful in the evaluation of intrauterine death risk, especially for monochorionic twins.
Thus, some one may argue that the birthweight percentile curve based on different chorionicity in different may not necessary, indeed, the bene t is probably prominent. It was reported that the incidence of stillbirth and neonatal deaths in smaller dichorionic twin small for gestational(SGA) was signi cantly higher compared with those non-SGA ones [17]. Besides, compared to dichorionic pregnancies, monochorionic pregnancies have a higher risk of adverse outcomes, such as stillbirth, neonatal deaths and morbidities, adverse neurodevelopmental sequelae [20]. Therefore it is indeed need to distinguish the SGA twins and give them intensive care, while give the non-SGA twins routine newborn care. The birthweight percentile curve based on chorionicity and gestational age of twin are helpful as a reference for perinatal health care professionals and researchers to identify the the high risk fetus and neonates who require special care and intensive observation [8]. Thus, using twin growth charts based on chrionicity is likely to prevent the over-diagnosis of SGA in normal growth twins.
Certainly, birth weight for gestational age is an important indicator of the adequacy of fetal growth. While, restricted fetal growth is likely in a causal pathway to all forms of Attention-De cit/Hyperactivity Disorder (ADHD) [16]. In this study, we found that the birthweight of monochorionic twins were lower than dichorionic, and most twins were lighter than singleton neonates in the same gestational age. It was reported that most infants delivered form multiple pregnancies are growth-restricted compared to singleton infants as a result of an adaptive process [4].Many authors underline the need for a separate estimation for multiples of a reliable range of normal values for fetal and newborn anthropometry [2; 5; Overall, our study con rmed the basic principle that neonatal birthweight rose up with grater slopes withe the progress of gestational age during the third trimester, which was reported in singleton and twin pregnancies [7; 8; 26]. In addition, we found that the calculated 50th percentile birthweight values of twin boys were higher than those for girls based on the same chorionicity, except monochorionic twins before 31 weeks gestational age. Previous research has extensively documented that boys were born heaver than girls in singleton pregnancies [14; 23] and most twin pregnancies [10]. Besides, the mean birthweight of dichorionic twins were heavier than monochorionic twins within the same sex, which had been reported in other studies based on different races [9]. In contrast, we found that the calculated values of the 50th percentile for monochorionic twin boys were lower than those for girls before 31 weeks gestational age. The reason of this incompatibility need to be research more.
Several limitations of present study deserved to mention. Firstly, this is a single center literature, which may suit for the local region. Secondly, the sample size was relatively small in monochrionic twin infants, due to the chrionicity ratios in twin pregnancies.

Conclusion
Neonates birthweight percentile chart based on sex and chrionicity provide a tool for assessing the well being of twin infants. Use twin growth charts based on chrionicity is likely to prevent the over-diagnosis of SGA in normal growth twins.

Study population
We retrospectively analysis the sex speci c live-birth twins birthweight based on different chorionicitiy in Guangdong Women and Children Hospital between 2015 to 2020. A total of 3431 twin neonates were enrolled into the study, including 366 monochorionic girls, 405 monochorionic boys, 1235 dichorionic girls and 1425 dichorionic boys. Each record included information about mode of delivery, neonatal sex, gestational age at birth, chorionicity, birth weight. All record information were collected from clinical record.
We included the live birth twins at the gestational age between 25 weeks and 40 weeks. The gestational age was estimated combined last-menstrual-period(LMP) and ultrasound scan in the rst trimester. The chorionicity was assessment by ultrasound scan before to 13 +6 weeks gestational age, combined the pathological examination of the placenta to determine the number of placenta or layers of amniotic and chorionic.

Ethical approval and informed consent
The study was performed in accordance with the approved guidelines and regulation. Ethical approval to Compared the twins neonatal parameters between different sex and chorinonicity in the same gestational age by t test after the normality test. All statistical test were carried out at 0.05 signi cance level.

Declarations Acknowledgement
The authors thank the Department of Department of Obstetrics and Medical Genetics Center staff members of Guangdong Women and Children Hospital; and the parents and their children who participated.

Author Contributions
The version to be published was approved by all the authors.all authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Jing Wu was responsible for research design and management. Qian Liu was responsible for case collection, data analysis, and article writing. Yanlin Huang was responsible for data analysis.