The Influence of a Male Twin on Birthweight of its Female Co-twin — A Population-based Study

Abstract

Fetal growth is influenced by various determinants, with males being heavier than females. It was recently suggested that female birthweight tends to be increased by the presence of a male co-twin. We evaluated this hypothesis in the Israeli population. We reviewed a retrospective population database of the 1993-1998 Israeli Birth Registry. We compared male birthweight in the male-male and malefemale combination sets and female birthweight in the femalefemale and male-female combination sets. We compared the mean birthweight of males and females in three groups of total twin birthweight. The sample of 12,686 sets included 50.6% males. The male-male combination was found in 31.3% sets, female-female in 38.7% and unlike-sex combination in 30.0%. A total twin birthweight of less than 3000g was found in 7.2% sets, of 3001-5000g in 50.7% sets, and of over 5000g in 42.1% sets. The mean male birthweight was 2398 ± 602 g and the mean female birthweight was 2316 ± 566g, p < .0001 (95% CI of 67, 96). The mean birthweight of males in the malemale combination was significantly lower than in the unlike-sex combination, p < .0001, in total birthweights over 3000g. No significant difference was found between the mean birthweight of females in the female-female and in the unlike-sex combinations in all total birthweight strata. Our findings do not substantiate a male-related inter-twin influence on female birthweight. Population differences might underlie the opposing observations in the literature.

The Natural Course of Monochorionic and Dichorionic Twin Pregnancies: A Historical Cohort

“…We did not find a tendency for birthweight in females to be influenced by the presence of a male co-twin. This is in agreement with two other studies (Goldman et al, 2003;Orlebeke et al, 1993).…”

Birth size and gestational age in opposite-sex twins as compared to same-sex twins: An individual-based pooled analysis of 21 cohorts

“…Our findings are in line with previous studies showing a difference of 57 g 10 , 64 g 11 and 78 g 12 , even when different inclusion criteria for SS twins were used. For girls, birth weight was very similar in SS and OS twins, which is also in agreement with these studies 10 – 12 . Boys with a co-twin sister were 0.16 cm longer than those with a co-twin brother, but differences were not significant in girls.…”

“…Some studies have shown that boys from opposite-sex (OS) pairs are significantly heavier at birth than boys from same-sex (SS) pairs 10 – 12 , but this difference did not reach significance in other studies 13 – 16 . The greater birth weight of boys from OS pairs has generally been ascribed to a more successful in utero competition for nutrients of boys in the presence of a sister rather than a brother co-twin 17 .…”

No “masculinization” effect of a male on birth weight of its female co-twin

“…A population-based study [7] then showed that females in unlike-sex twin pairs are signifi cantly heavier than females from like-sex pairs or female singletons, implying that an inter-twin mediator might exist; produced by the male that somehow affects the female co-twin despite the presence of a dichorionic placenta. Blumrosen and her co-workers [3] suggested that in severely discordant twins, the larger females were not signifi cantly heavier, an observation which might support the hypothesis of some form of gender-dependent intertwin infl uence.…”