Heritability of parturition timing: an extended twin design analysis.
OBJECTIVE
The objective of the study was to assess relative maternal and paternal genetic influences on birth timing.


METHODS
Utilizing The Netherlands Twin Registry, we examined the correlation in birth timing of infants born to monozygotic (MZ) twins and their first-degree relatives (dizygotic twins and siblings of twins). Genetic models estimated the relative influence of genetic and common environmental factors through model fitting of additive genetic (A), common environmental (C), individual-specific environmental factors, and combinations thereof.


RESULTS
We evaluated birth timing correlation among the infants of 1390 twins and their 644 siblings. The correlation in MZ female twins (r = 0.330) was greater than MZ male twins (r = -0.096). Positive correlation were also found in sister-sister pairs (r = 0.223) but not in brother-brother (r = -0.045) or brother-sister pairs (r = -0.038). The most parsimonious AE model indicated a significant maternal contribution of genetic and individual-specific environmental factors to birth timing, but no paternal heritability was demonstrated. Heritability of birth timing in women was 34%; and the remaining variance (66%) was caused by individual-specific environmental factors.


CONCLUSIONS
Our data implicate a significant contribution of maternal but not paternal genetic influences on birth timing.
Kistka
Zachary A-F
ZA
Department of Pediatrics, Washington University, St Louis, MO, USA.
DeFranco
Emily A
EA
Ligthart
Lannie
L
Willemsen
Gonneke
G
Plunkett
Jevon
J
Muglia
Louis J
LJ
Boomsma
Dorret I
DI
D000328:Adult; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D036801:Parturition / Q000235:genetics*; D012737:Sex Factors; D013997:Time Factors; D014427:Twins / Q000235:genetics*; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics