Title: Sex Distribution of Newborns to Mothers With Systemic Lupus Erythematosus
Abstract: To the Editor: The sex of newborns is distributed almost equally between girls and boys. Some reports have suggested that environmental factors influence the newborn sex distribution.1 Furthermore, there are reports of fetal sex predominance associated with some pregnancy complications such as female predominance among patients with hyperemesis gravidarum and male predominance in patients with preeclampsia.2,3 Among adults, diseases can be specific to sex; for example, systemic lupus erythematosus (SLE) has a female predominance of 9:1 among people in their childbearing years.4 Moreover, SLE has the capacity to affect the course and outcomes of pregnancy. Information on the sex distribution of newborns is generally lacking in studies investigating pregnancy outcomes of women with SLE. Those reports are limited by a relatively low number of pregnancies and the selective nature of the study populations. One study5 reporting the sex of newborns to women with SLE showed a 53.6% male rate (15 of 28) in live newborns. The objective of the present study is to compare the sex distribution between infants born to mothers with SLE and the general population. We performed a retrospective population-based study that included all deliveries occurring during the period 1988–2003 at Soroka University Medical Center, the only regional medical center with a delivery room in Southern Israel, serving a population of 800,000 residents. Patients with SLE were compared with patients who did not have SLE. Patients with other connective tissue disorders or with lack of prenatal care were excluded from the analysis. During the study period, of 164,885 live-born deliveries to 68,600 women, 91 live deliveries were reported to 42 women ever diagnosed with SLE; 68 (75%) occurred after the women were diagnosed with SLE. The sex distribution of newborns showed a male predominance of 69% (95% confidence interval = 59–78%), compared with 51.2% (50.9–51.4%) in the general population. This pattern remained consistent before and after the SLE diagnosis (61% and 71%, respectively). Eighteen percent of women were delivering for the first time (16/91), whereas 25 (28%) had 2 deliveries, 26 (29%) had 3 deliveries, and an additional 24 (26%) had 4 or more deliveries. The proportion with previous infertility treatment was 2% both for mothers with and mothers without lupus. A history of 3 or more miscarriages was considerably higher in women with SLE compared with other mothers (19% vs 6%). The incidence of preterm delivery and small for gestational age (SGA) was also higher among patients with SLE (43% and 15% among mothers with SLE compared with 19% and 12% among mothers without SLE). The higher incidence of pregnancy complications among patients with SLE, including repeated miscarriages, SGA, and preterm delivery, is in accord with previous reports.6,7 We found a strong predominance of boys in the population of offspring born to mothers with SLE. We hypothesize that female fetuses are more affected by the maternal SLE, just as SLE is more common among women, in general. The study is limited by our ability to ascertain only the sex of live births. Thus, we cannot be certain that the aborted fetuses in the group of women with SLE were predominantly females. Larger cohorts are needed to confirm this finding and to explore mechanisms that might be responsible for an adverse effect of maternal SLE on female fetuses. To confirm our hypothesis of a higher rate of spontaneous abortion of female fetuses in mothers with SLE, sex distribution in fetuses at an early stage of the pregnancy should be compared with the respective distribution in newborns. Victor Novack Department of Medicine and Department of Epidemiology Soroka University Medical Centre Ben-Gurion University of the Negev Beer-Sheva, Israel [email protected] Offer Erez Department of Obstetrics and Gynecology B Lena Novack Department of Epidemiology Alan Jotkowitz Department of Medicine Amit Meir Moshe Mazor Department of Obstetrics and Gynecology B