Background Prematurity postpones the birth of a subsequent sibling. This phenomenon is strongest in mothers with long prior interbirth interval, a proxy of fertility problems.
Aim We assessed whether a history of miscarriages explains the postponed birth of next sibling after preterm birth.
Methods We obtained pregnancy and newborn data from Finnish Medical Birth Register (Jan 1, 1987 - Sep 30, 1990). Sibling data came from the National Population Register Centre.
Of the total of 230378 singleton births we excluded 1242 (0.5%) due to death before 1 yrs. GA was missing for 2922 (1.3%) and miscarriage data for 2964 (1.3%); 225650 children remained in analyses.
We utilised Cox regression for proportional hazards to analyse the effect of GA and history of miscarriages on sibling birth.
Results A low GA at birth delayed subsequent sibling birth. The effect remained unchanged after introducing miscarriages in the model.
*Numbers indicate completed gestational weeks. HR, Hazard Ratio (term group, females and no miscarriages as a referent).
Conclusions Prematurity postponed subsequent sibling birth. Accounting for obstetric history left this effect unchanged.