Birthweight of Full-Term Twin Infants in Relation to Sex-Pair

Introduction

Growth rate in twins tend to be normal up to 30–34 weeks of gestation, when they attain a combined weight of 4000 grammes.1 Subsequently, they grow more slowly.1 Birthweight is the single most important determinant of perinatal morbidity and mortality.2, 3 In twin gestations, abnormal growth in one or both twins contributes to the increased morbidity and mortality observed in such pregnancies.4 Two common growth abnormalities associated with poor perinatal outcome are intrauterine growth restriction and intrapair birthweight discordance.5 Twin gestation is known to have a negative influence on birthweight.1 In Nigeria, for instance, the reported incidence of delivery of a low birthweight (birthweight less than 2500 g) infant in twin gestation varied from 49.8%6 to 66.2%7 compared to 8.1%8 to 9.53%9 among our general obstetric population. In a recent study in Nigeria, the reported incidence of intrapair birthweight discordance was 28.8%.10

Abstract

BACKGROUND

Nigeria has one of the highest twining rates in the world. Twin gestation is known to have a negative influence on birthweight but the effect of sex-pair is not well established.

OBJECTIVE

To determine the effect of sex-pair on birthweight of twins.

METHODS

The birthweights and sex-pairs of 104 live-born full-term twin pairs were recorded and analyzed. The mean birthweight of different-sex twin pair was compared with that of same-sex twin pair. Also the mean birthweight sum of different-sex twin pair was compared with that of same-sex twin pair. The relative incidence of low birthweight (LBW) and birthweight discordance in different-sex twin pair and same-sex twin pair were examined.

RESULTS

Comparing the mean birthweight of different-sex twin pair with that of same-sex twin pair, it was 2503±428g (95% confidence interval, CI: 2369–2637) versus 2398±442g (95% CI: 2291–2505), t=0.851, P>.05. The overall mean birthweight sum of different-sex twin pair was 3889±492g (95% CI: 3679–4099) while for same-sex twin pair it was 3665±512g (CI: 3493–3837), P>0.05. The mean birthweight sum for male-male twin pair was 3903±536g (95% CI: 3648–4158), while that of female-female twin pair was 3426±560g (95% CI: 3160–3192), P<0.05. The mean birthweight of female infants in male-female twin pair was 2081±492g (95% CI: 1703–2459) compared to 1795±502g (95% CI: 1635–1955) for female infants in female-female twin pair, P>0.05. The figures for the male infants in male-female pair and male-male twin pair were 2136±468g (95% CI: 1945–2327) and 1976±519g (95% CI: 1804–2148), respectively, P>0.05. Frequency of delivery of LBW twin pairs were: (1) different-sex 51.3%, (2) male same-sex 43.8%, and (3) female same-sex 75.8%. Out of 59 LBW twin pairs, 20 (33.9%) were different-sex twins pair while the remaining 39 (66.1%) were same-sex twin pairs. Of 30 birthweight discordant pairs, 12 (40.0%) were different-sex twin pair while 18 (60.0%) were same-sex twin pair, corresponding to a ratio of 1:1.5.

CONCLUSION

In twin gestations, cohabitation in utero of fetuses of different gender influenced their intrauterine growth.

Keywords

Birthweight, intrauterine growth, twin gestations, sex-pair