Pregnancy in Essential Thrombocythemia (ET): Experience with 40 Pregnancies.

40 pregnancies of 16 women with ET were analyzed retrospectively. In 6 patients ET was diagnosed before the first pregnancy. In 10 patients thrombocytosis was detected for the first time during a pregnancy, and the diagnosis of ET was confirmed in the median of 17 months from the delivery. Of the pregnancies 45% (18/40) were complicated, 55% (22/40) uncomplicated, and 63% (25/40) resulted in live birth. 9/16 women had at least one complicated pregnancy. The most common complication was spontaneous abortion during the first trimester, seen in 33% of all pregnancies and comprising 72% of all complications. 2 intrauterine fetal deaths occurred at weeks 22 and 28. 3 pregnancies were complicated by eclampsia or pre-eclampsia. The non-pregnancy-related symptoms of ET or platelet counts before conception or during pregnancy did not correlate with the risk of complications. The median of maximum platelet counts during the first trimester in 16 pregnancies resulting in live birth was 757 x 10⁹/l (255 – 1561 x 10⁹/l) and in 13 pregnancies ending in pregnancy loss 835 x 10⁹/l (697 – 1525 x 10⁹/l) (p=0.25). The intrauterine fetal deaths occurred with platelet counts 553 and 574 x 10⁹/l. In patients with eclampsia or pre-eclampsia the platelet counts were normal at the onset of the symptoms. Only 2 patients had other ET-related symptoms during pregnancy. 9 patients had ET-related symptoms before or between the pregnancies. In 4 of them the pregnancies were uncomplicated. Treatment for ET was or had been given to 11/16 (67%) women in 13 pregnancies either during the pregnancy or before conception or both. Acetylsalicylic acid (ASA) was given in 10 pregnancies of 9 patients. 2 continued with ASA throughout the pregnancy. In 7 patients ASA was started at 4–27 weeks of gestation, in 4 of them during the first trimester. 7 patients had received platelet lowering drugs before conception. 5 were on interferon (IFN) before conception; 3 of them switched over to ASA after conception, one continued with IFN after a 4-week break from week 15 onwards, one continued with IFN throughout the pregnancy. Both patients on IFN during the pregnancy received also ASA. 2 women had been treated with busulphan before conception; one because of previous recurrent miscarriages successfully before two pregnancies, and the other with no pregnancy planning 26 months before the conception. Pregnancy complications occurred in 18/27 (67%) pregnancies in women without any treatment and in 0/13 pregnancies in those with treatment before or during the pregnancy (p<0.001). The live-birth rate in the treated patients (13/13 pregnancies, 100%) was higher than that in the untreated patients (12/27 pregnancies, 44%)(p<0.001). 8/8 pregnancies with ASA alone resulted in live birth (difference from untreated patients p=0.01). Conclusion: Nearly half of the pregnancies in patients with ET were complicated and one third resulted in pregnancy loss. Treatment with ASA alone during pregnancy or platelet-lowering drugs before or during pregnancy was associated with lower risk of complications.