Fig. 1.

Recurrence risks of preterm birth (PTB) (Figure courtesy of Dr. Joe Leigh Simpson). (A) Women whose first deliveries were preterm have a higher chance of PTB in their second deliveries, especially when the first deliveries had shorter gestations [2]. (B) Mothers who themselves were born preterm have an increased risk of PTB [4]. (C) PTBs to a woman's mother, full sisters, or maternal half-sisters increase her PTB risk, whereas PTB in her paternal half-sisters or in members of her partner's family do not affect her risk [5].