Fetal growth in India : studies on antenatal prediction of low birthweight and some factors that determine birthweight

Abstract

Objectives: To develop standards for assessment of fetal growth in India and to study some factors that determine birthweight.

Methods: Data from 250 normal pregnancies were used to construct graphs of fundal height, abdominal girth and the ratio of fundal height to abdominal length. These graphs were used to predict light for gestational age (LGA) infants in 150 high-risk and 208 low-risk pregnancies. Gestation specific fundal height measurements predictive of LGA were calculated from the above data. A tape measure with these 'cut off measurements marked was then used in 253 women to screen for LGA. A group of 994 singleton live born infants and their mothers were studied and exposure to tobacco during pregnancy was ascertained by interview. Another 200 women were screened for genital mycoplasma infections by vaginal and endocervical cultures at 26-30 weeks and again at 36-38 weeks of pregnancy. Sonographic fetal biometry was carried out in 120 pregnant women at regular intervals from 20 weeks until delivery. A similar study was carried out in 41 ethnic Fijians and 40 ethnic Indians in Fiji. Smoothed gestation-, sex- and birth order- specific birthweight centiles were calculated from data from 11,645 singleton live births. Smoothed gestation-specific birthweight centiles without adjustments for sex and birth order were then calculated for all 10,540 infants born between 37 and 41 weeks. Data for births between 37 and 41 weeks were reanalysed using non-adjusted and adjusted centiles.

Results: Fundal height measurements had high sensitivity (77-84%) and specificity (79-88%) in screening for LGA. Infants of passive smokers were on average 55 lighter than infants of non-smokers. Passive smoking was associated with a decrease in birthweight of 63 g (95% CI 12 -114 g) after adjusting for other variables known to affect birthweight. Forty (20%) women were infected with mycoplasma and 79 (39.5%) with ureaplasma at either site or either time. No significant differences were noted between infected and uninfected women in birthweight or gestation at delivery. Fetal biparietal diameter and femur length in Indian and European fetuses were similar but abdominal circumference grew at a slower rate in the Indian fetus after 28 weeks. The median gestation at delivery was 39 weeks. In Fiji, growth rate of the abdominal circumference was slower in Indian fetuses. Indian infants were on average 795 g lighter and had a 5.5 days shorter mean length of gestation. Ethnicity of the mother was associated with a 0.11 cm (95% CI 0.03-0.19) difference in growth rate of the abdominal circumference after adjusting for other factors known to influence fetal growth. Significant misclassification of infants occurred based on birthweight alone (P < 0.001).

Conclusions: Fundal height measurement was a reliable method screening for LGA. Passive smoking was associated with a decrease in birthweight but genital mycoplasma infections were not. Indian fetuses had a slower growth rate of abdominal circumference and were born at an earlier period of gestation. Adjustments for sex and birth order were required for proper classification of birthweight.