The Effect of Biological Factors on Birth Weight and Gestation in South Indian New-Borns

Background: Understanding the effect of biological factors on birth weight of new-borns has public health importance because these indicators are associated with infant health and survival and influence development and health in later life. Aim: The study was undertaken to determine the birth weight and gestational age characteristics in south Indian babies and correlated to biological factors. Settings and design: A retrospective study of consecutive singleton live births, who delivered in the hospital in a metropolitan city of Bangalore, South India. Materials and methods: A cohort of singleton live births, born from January 2015 to May 2017 were analysed to determine the mean birth weight and gestation and influence of various biological factors such as gender of baby, birth order, mother’s age, obstetric complication such as PIH and Diabetes etc. Results: Among a total of 2789 singleton live births, the mean birth weight was 2873.73 ± 498.6 g, mean gestation was 38.2 ± 2 weeks and Low Birth Weight (LBW) <2500 g was 19.1%. The Term, male, later births, older mothers above 30 years and pregnancy of Pregnancy Induced Hypertension (PIH) and diabetes were associated with statistically significant higher birth weight P=0.001, P=0.002, P=0.0001, P=0.001, P=0.0006 and P=0.0001, respectively. Conclusion: The mean birth weight and gestation for singleton live births in South India were determined, as well as the statistically significant impact of various biological criteria.


Introduction
Birth weight is one of the most important factors that predict the survival, future development and growth pattern of a new-born baby [1][2][3][4][5]. Birth weight is mainly influenced by duration of gestation but other biological factors such as gender, birth order, mother's age, obstetric complications etc. also play a role. The present study was undertaken in a Speciality hospital in Bangalore, South India to determine the average birth weight and gestation as well the positive correlation of biological factors including complications of pregnancy such as PIH and Diabetes.

Materials and Method
All 2789 singleton live born babies included in this study among a total 2808 consecutive births from January 2015 to May 2017, at Shifaa Hospital, a multispecialty center catering mainly to the middle and lower socioeconomic strata, in the metropolitan city of Bangalore. Exclusion criteria were 19 twin deliveries and 18 stillbirths. All women received adequate prenatal care and gestational age assessed by Last Menstrual Period (LMP) correlated with Crown-rump length (CRL) measurement by ultrasound examination undertaken within 18-20 weeks to establish fetal age when menstrual dates were unknown or in pregnancies with discrepancy greater than ± 7 days. If CRL and menstrual dates agreed to within the normal range of error (± 7 days), then LMP was used to establish fetal age. Birth weight was recorded within 24 h of birth on a digital weighing machine accurate up to 10 g. Sources of data were Labor room register, new-born register and maternal and neonatal records when required. Data was entered into EPIDATA entry software, 3.1.2701.2008 and data analysis with statistical significance was done using STATA version 13.1.

Results
There were a total of 2808 deliveries during the 29 month period from 1st Jan 2015 to 31st May 2017, exclusion criteria were 19 twin deliveries and 18 stillbirths. Among the 2789 singleton live births included in the study, birth weight was missing for 2.9% (n=81), gestation was missing for 8.9% (n=251), gender was missing for 3.7% (n=105), birth order was missing for 4.1% (n=116) and mother's age was missing for 7.3% (n=206).
The incidence of obstetric complications of Pregnancy Induced Hypertension (PIH) was 5% (n=136) and Diabetes 4.6% (n=124). Most infants 32.3% (n=44) with obstetrical complications of PIH and 35.4% (n=44) with maternal diabetes weighed between 3000-3499g. The mean birth weight with and without PIH complicating pregnancy was 2730 ± 511 g and 2881 ± 496 g, respectively, the difference of 151g being highly statistically significant (P=0.0006). However infants of diabetic mothers weighed more, mean birth weight 3039 ± 455 g compared to 2853 ± 515 g in non-diabetic mothers, a difference of 186 g, was highly statistically significant (P=0.0001).
According to UNICEF LBW rates were 7%, 16% and 19%, respectively in industrialized, developing and least developed countries [6]. LBW and preterm birth rates were 17.0% versus 5.5% and 12.3% versus 6.9%, respectively in South India and Nova Scotia, Canada [7]. Unlike in Western countries, where the incidence of LGA babies has spiralled upward, it has remained nearly at the same level over one and a half decades, reported in South India, despite improvements in socioeconomic status and obstetric care, the mean birth weight 2846 g in 1996 remained at 2907 g in 2010 over 15 years, with a difference of only 61 grams [5,7]. Thus Indian women will continue to have a high incidence of LBW up to 27.4% reported in rural India [8] though it is unclear whether high rates of LBW in South Asia are due to poor fetal growth or short pregnancy duration [9]. In contrast western population report a high mean birth weight of 3446 g in U.S born white women, a difference of 573 g compared to the present study [10]. Globally of the 20 million LBW representing 15.5% of all births, 95.6% are in developing countries with India alone accounting for 40% LBW in developing countries [11], however in developing countries the majority of LBW new-borns have intrauterine growth restrictions rather than being born preterm [12] hence a redefinition of LBW is indicated in ethnic Asians so as to more accurately identify prematurity as cause of LBW [12].
Sex ratio was 984 females to 1000 male infants; a skewed 804 female/1000 male infants was reported from North India [4]. Male babies had higher mean birth weight of 2916 ± 501 compared to female babies with 2835 ± 481, difference of 81 g being highly statistically significant (P<0.0001), similarly also reported in another study male weighed 45 g more than female babies, mean birth weight being 2934 g and 2889 g, respectively [4]. However more males 12.6% (n=160) were born preterm <37 weeks, compared to females 10.3% (n=130). The mean gestation in males and females being 38.3 ± 1.7 and 38.4 ± 1.6 respectively also statistically significant (P=0.02).
First births were lighter with mean birth weight of 2817 ± 4 84 g compared to 2899 ± 503 g in later born infants, difference of 82 g being statistically significant (P=0.0001). However more 12.8% (n=220) later births were preterm <37 weeks, compared to 8.9% (n=75) first birth infants, with a mean gestation of 38.2 ± 1.6 weeks and 38.5 ± 1.5 weeks, respectively being statistically significant (P<0.001). Other study also reported later birth infants being heavier by 100g with the mean birth weight of 2880 g compared to 2770 g for first born babies [4].
Caesarean section rate increased to 41.6%, majority being emergency section 64.7% and in 35.2 % elective or planned sections. Repeat section was performed in one third 32.6%. In contrast other studies report a low cesarean rate of 15.3% in North India [4] and 3.1% in 1986-87 increasing to 10.9% in 2004-2005 in South India while in Nova Scotia, Canada it increased from 20.2% to 28.4% [5]. Understandably though emergency cesarean section delivery was related to a higher incidence of prematurity 16.5% compared to 11.4% among elective sections, the mean gestation between emergency and election sections was not statistically significant (P=0.94), contrasted with mean gestation of 38.5 ± 1.6 weeks in infants with normal delivery compared to 38.1 ± 1.6 C.S being statistically significant (P<0.001). in contrast infants of normal delivery had lower mean birth weight of 2848 ± 477 g to 2850 ± 529 g in caesarean births, difference of 19g being statistically significant (P=0.047). A higher incidence of LBW 22.1% was noted for emergency sections compared to14.8% in elective sections. Thus the risk for LBW and prematurity was higher with emergency sections.
Obstetric complications of PIH and Diabetes had higher incidence of prematurity 24.8% and 21.9%, respectively with mean gestation of 37.5 ± 2.0 weeks and 37.7 ± 1.4 weeks respectively compared to 38.4 ± 1.6 weeks in uncomplicated pregnancy of statistical significance (P<0.001). Similarly a low mean birth weight of 2730 ± 511 g in infants with PIH complicating pregnancy contrasted with higher mean birth weight of 3039 ± 455 g in infants of diabetic mothers, in contrast pregnancy uncomplicated with PIH and diabetes had mean birth weight of 2881 ± 496 and 2853 ± 515 g, respectively, this difference of 151 g and 186 g, respectively being highly statistically significant (P=0.0006) in the former and (P<0.001) in the latter.

Conclusion
Mean birth weight is a good indicator for any population to determine outcome of new-borns. This study reveals that though duration of gestation had a major impact on birth weight other biological factors such as gender with male babies, second and later births, as well as infants born to older mothers tended to have statistically significantly higher mean birth weight. In contrast infants of mothers with PIH registered lower mean birth weight to infants of diabetic mothers with higher mean birth weight but significantly shortened gestation.
Mean birth weight is a good indicator for any population to determine outcome of new-borns. This study reveals that though duration of gestation had a major impact on birth weight other biological factors such as gender with male babies, second and later births, as well as infants born to older mothers tended to have statistically significantly higher mean birth weight. In contrast infants of mothers with PIH registered lower mean birth weight to infants of diabetic mothers with higher mean birth weight but significantly shortened gestation compared to uncomplicated pregnancy.

Funding
No External Funding.