Our results answer 4 important questions regarding the association between pregnancy and POTS. First, no clinically important differences were noted between parous and nulliparous women in clinical presentation, autonomic testing, or laboratory evaluation. Second, the adverse event rate for mother and child during pregnancy in patients with POTS was similar to that seen in the general public. Third, autonomic evaluation showed a trend toward improvement but was not significant when comparing data before and after pregnancy. Finally, a nonsignificant trend toward improvement in OI was noted in the second and third trimesters.
Our study has 2 major limitations. The first is the lack of data for method of delivery and is related to the difficulties encountered in retrospective studies. Data on method of delivery (ie, spontaneous vaginal delivery, cesarean section) were not captured in most available records. Therefore, a reliable estimation of frequency per birth for a particular method of delivery was not possible. This was confounded because, when an adverse event occurred, data were consistently present. This would have likely led to a possible association between cesarean section and adverse outcomes, which would be misleading.
Of note, one of the women in the parous group opted for a planned cesarean section solely on the basis of her prior POTS diagnosis. Ultimately, the question of method of delivery is important and will likely require future prospective studies to provide an answer.
The second limitation is the lack of standardized data on clinical autonomic testing and symptom profiles during pregnancy. Standard autonomic testing is noninvasive, safe, and performed on pregnant women (with the exception of the TST) at our center (Autonomic Disorders Center, Mayo Clinic) when clinically necessary. However, standardized control values do not exist for pregnant women.10,12
Therefore, our data cannot be compared to those of pregnant women who do not have POTS.
Interestly, a significant difference in age (33.6 vs 29.6 years) and disease duration (3.7 vs 2.1 years) was noted between parous and nulliparous women, respectively. The age of parous women was higher than that previously reported at 30.2 years, but disease duration was similar to that previously reported at 4.1 years.2
However, approximately 20% of the patients in the study by Thieben et al2
were male. The difference in age most likely reflects the fact that pregnancy increases in frequency with age, and it could be argued that this is an expected result given the study design. However, the statistically significant differences we report in age and disease duration are highly unlikely to have any clinical importance in regard to either treatment or prognosis, particularly because the clinical characteristics and autonomic study results did not differ between groups.
The adverse events reported during pregnancy in our POTS cohort (total fetal complications, 9%; miscarriages, 7%) are similar to previously reported miscarriage rates of approximately 8% in the general public.17
Of the other 2 fetal complications, 1 was placenta previa with subsequent miscarriage, which would have only increased the frequency of miscarriage in our study to 8%, still comparable to rates in the general population and to that previously published in patients with POTS.9
The other complication was placental abruption and malpresentation, resulting in a healthy newborn but an obligatory hysterectomy for the mother (the only known maternal complication). We were surprised that maternal complications were minimal. Our prior clinical impression was that some of these women would have difficulty with OI during delivery and immediately postpartum. Even more conservative measures, such as intravenous fluid rehydration, for treating POTS-related symptoms were not found in the available clinical records. This may be related to our data showing a trend toward improvement in several autonomic parameters in the later trimesters and in the short-term postpartum period.
Changes in the cardiovascular system of pregnant women are substantial, reaching a maximum in the middle of the second trimester and continuing through the third trimester. These result in decreased systemic vascular resistance, increased cardiac output, and a large increase in plasma and blood volume.18
Blood and plasma volume can increase as much as 40% and 45% to 55%, respectively, compared with prepregnancy levels.19
These changes may underlie the trend we observed toward improvement in OI during the second and third trimesters. This would be comparable to the mainstays of conservative treatment of POTS (increased fluid and salt intake) aimed at increasing plasma volume and resulting in clinical improvement.20