Frequency of and risks associated with syncope in pregnancy

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Syncope is significantly associated with cardiovascular disease and pregnancy is known to causes changes in the cardiovascular system, but data are limited on incidence of syncope in pregnancy. Canadian researchers recently aimed to fill that knowledge gap by looking at temporal trends in incidence of syncope during pregnancy, neonatal outcomes associated with the condition, and frequency of syncope after delivery.

Data for the study, published in The Journal of the American Heart Association,were from all live births in the province of Alberta, Canada between January 1, 2005 and December 31, 2014. After excluding women who were not residents of Alberta; women with preexisting diabetes mellitus, cardiovascular disease, or other preexisting medical conditions; and births with incorrect or incomplete data, the final study population consisted of nearly a half million live births and pregnancies.

Syncope was reported in 4,667 of the 481,930 pregnancies (9.7 per 1000 incidence). The incidence rate of the condition during pregnancy increased from 7.6 per 1000 in 2005 to 11 per 1000 in 2014 (equivalent to an age-adjusted 5% increase per year (RR 1.05, 95% CI, 1.04-1.06; P<0.01). 

Compared with women without syncope, women experienced it were younger (age < 25 years; 34.7% vs 20.8%, P < 0.01), less likely to be married (57.7% vs 69.8%; P < 0.01) and had higher rates of medical conditions (1.8% vs 1.0%; P < 0.01). They were also likelier to have a history of syncope before pregnancy than women who did not experience it (11.5% vs 3.2%; P < 0.01).

In regard to timing, most women experienced their first episode of syncope in the second trimester (32.2 % in the first trimester, 44.1% in the second trimester, and 23.6% in the third trimester). Overall, 8% of pregnancies had more than one episode of syncope. 

In terms of neonatal outcomes, rates of preterm birth (PTB) were higher in women who experienced an episode of syncope than among women who did not have an episode (16.3% vs 15.0%, P< 0.01). Furthermore, women who experienced a syncope episode in the first trimester had the highest rates of PTB (18.3%) when compared to episodes in the second (15.8%) and third (14.2%) trimesters.

Over a median follow-up period of 4.6 years for children of pregnancies with syncope and a follow-up period of 5.1 years for children of pregnancies without syncope, the authors noted that rates of congenital anomalies were higher in the syncope group (3.1%) than in the non-syncope group (2.6%; P = 0.023). Pregnancies with syncope episodes in the first semester had the highest rates of congenital anomalies among children (3.4%). 

The authors believe their findings are important to identify women who may need closer monitoring during pregnancy and children who may need monitoring following birth. This is especially true for women who experienced episodes of syncope during the first trimester since rates of PTB were higher for these pregnancies. The other important finding from this study is that incidence rates for syncope increased over the study period. However, the authors believe future studies are needed to identify the potential causes for this trend.