Elsevier

Obstetrics & Gynecology

Volume 96, Issue 6, December 2000, Pages 986-990
Obstetrics & Gynecology

Adaptive growth restriction as a pattern of birth weight discordance in twin gestations

https://doi.org/10.1016/S0029-7844(00)01079-6Get rights and content

Abstract

Objective: To challenge the hypothesis that discordant growth is a normal variation by relating birth weight discordance to total twin birth weight.

Method: Among 12,565 Israeli live-born twin pairs (1993–98), we compared total twin birth weight decile, the frequencies of three levels of discordance in the general population, over 25% discordance between like- versus unlike-sex pairs, and over 25% discordance between pairs delivered by primiparas versus multiparas.

Results: We found a marked change in the best-fit correlation function with increased discordance: level 15–24.9% was inversely linear whereas levels 25–34.9% and over 34.9% were inversely logarithmic (R2 = .47, .88, and .9, respectively). The best-fit correlation of frequencies of more than 25% discordance was inversely logarithmic and similar in like- and unlike-sexed twins across deciles functions (P = .7, odds ratio [OR] 1.0, 95% confidence interval [CI] 0.9, 1.2). The overall frequencies of discordance were also similar (9.3% versus 10.2%, P = .11, OR 0.9, 95% CI 0.8, 1.0). The frequencies of primiparas decreased linearly (R2 = .98) and the frequencies of more than 25% discordant pairs in multiparas and primiparas across the deciles had similar inversely logarithmic patterns (P = .55, OR 1.0, 95% CI 0.9, 1.2). Discordance over 25% was significantly more frequent among primiparas (P < .001, OR 1.45, 95% CI 1.3, 1.6).

Conclusion: The observed patterns of birth weight discordance did not substantiate normal variation but an adaptive growth restriction that might explain why the likelihood of discordant growth decreases as total twin birth weight increases.

Section snippets

Patients and methods

We used data from the Israeli Birth Registry through the Central Bureau of Statistics, which includes all deliveries in Israel, as required by law. The database of 12,785 twin pairs delivered from 1993–1998 was used to select a cohort of 12,777 pairs (99.9%) with known birth weights and genders. Maternal parity was known in 12,565 (98.3%). The range of maternal age was 18–44 years, the range of parity 0–7. All women were Israeli citizens, roughly comprising 80% Jewish, 15% Moslem, and 5% other

Results

Frequencies of the variables studied are shown in Table 1. The numbers of discordant pairs in the categories 15–24.9%, 25–34.9%, and 35% or more were plotted as functions of the total twin birth weight deciles. The best-fit correlation for discordance level 15–24.9% was inversely linear (percentage of discordant twin pairs = −0.44 [decile order] + 21.8) but with a relatively low R2 value of 0.47 and the slope was not different than zero (P = .02; 95% confidence interval [CI] for the slope −.8,

Discussion

We used an epidemiologic approach to differentiate between patterns of discordant growth in twins. There is evidence that frequencies of divergent birth weight have a pattern based on total twin birth weight, suggesting that the greater the uterine capacity to nurture twins is, the smaller the likelihood of birth weight discordance.1

The first aspect we examined was the transition from low- to high-level birth weight discordance. Figure 1 shows that with more than 25% discordance, there is an

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