Table 2.

Genome‐wide association studies of preterm birth

Authors	Category of preterm birth	Sample size	Limitation	Concerns
Zhang et al., 2015	<34 weeks gestation (spontaneous onset of labor)	1,851 (916 cases)	Small sample size	Reduces power
			Inclusion of highly heterogeneous groups (in terms of ancestry)	Further reduces power
			Lack of stringent control for background ancestry	Increases false‐positive rate
			Lack of support from markers in the same chromosomal regions	Increases probability of genotyping errors
			Failure of replication in independent samples	Suggests unreliable results
Rapport et al. 2018	Birth between 25 and 30 weeks gestation (spontaneous onset of labor)	13,944 (1,349 cases) split into five ancestral groups EUR 9,890 (260 cases) AFR 1874 (190 cases) AMR 1847 (745 cases) EAS 249 (131 cases) SAS 59 (23 cases)	Each association was only observed in one of the five samples
			Unable to obtain replication in any external samples	Suggests unreliable results
			Samples from which the associations were seen were small (AFR N preterm = 190, AMR N preterm = 745)	Reduces power
			Each subsample was genetically heterogeneous, controlling for ancestry challenging	Further reduces power
			Cases and controls were taken from different populations	Possible genotyping batch effects