Table 4.

Genetic approaches to dissecting maternal and fetal contributions to birth timing

Contribution of genetics to birth timing
Group	Approach	Fetal genes	Maternal genes	Summary	Covariates	Reference
Boyd et al.	Population epidemiology	-	++	Women with a history of preterm birth (mothers, full sisters, or maternal half-sisters delivered preterm) were 55% more likely to deliver preterm	Yes	[13]
York et al.	Children of twins	+	+	Both maternal and fetal genetic effects contribute to gestational age	No	[33]
Clausson et al.	Children of twins	N/A	+	The heritability for preterm birth is approximately 36%	No	[34]
Lunde et al.	Population epidemiology	+	+	11% of variation in gestational age can be explained by fetal genetic factors Maternal genetic factors account for 14% of the variation in gestational age	Yes	[35]
Kistka et al.	Children of twins	-	++	Maternal genetic factors may contribute up to 34% of variation in the timing of birth	No	[37]
Wilcox et al.	Population epidemiology	-	++	Mothers born preterm have a higher risk for preterm delivery whereas preterm fathers do not affect likelihood of child being born preterm. This suggests that paternal genes have little effect on preterm delivery risk, arguing against fetal genetic contributions	Yes	[36]
Plunkett et al.	Segregation analysis	+	++	The maternal genome and possibly maternally inherited fetal genes influence birth timing	No	[38]

-, No evidence for genetic contribution; +, moderate genetic contribution; ++, strong genetic contribution.