Association of chronic hypertension with birth of small-for-gestational-age neonate

Objective: To examine the effect of chronic hypertension (CH), with and without superimposed preeclampsia (PE), on the incidence of small for gestational age (SGA) neonates, and explore possible mechanisms for such association.

Methods: The data for the study were derived from prospective screening for adverse pregnancy outcomes in women with singleton pregnancies attending for their first routine hospital visit at 11-13 weeks’ gestation, which included recording of maternal characteristics and medical history and measurement of mean arterial pressure (MAP). Birth weight z-score, adjusted for gestational age and for maternal and pregnancy characteristics, and incidence of SGA were compared between those with and without CH in the total population and in the subgroups with and without PE. Regression analysis was used to examine the relationship between MAP and birth weight z-score and incidence of SGA and PE in those with and without CH.

Results: The study population constituted 74,226 pregnancies, including 1,052 (1.4%) with CH and 73,174 without CH. Preeclampsia developed in 233 (22.1%) cases of the group with CH and in 1,662 (2.3%) of those without CH. In the group that developed PE, there was no significant difference between those with CH and those without CH in either the median birth weight z-score or the incidence of SGA. In the group without PE, the incidence of SGA was twice as high in those with than in those without CH. There was a significant association between log10 MAP multiple of the median and incidence of SGA and PE which was more marked in those with CH than in those without CH.

Conclusion: CH is associated with increased risk of SGA and PE and this is related to MAP at 11-13 weeks’ gestation.