BACKGROUND AND PURPOSE:

• Gestational thrombocytopenia is defined as platelet count < 150,000 per cubic millimeter (see ‘Related ObG Topics’, below)
• However, data on platelet counts throughout pregnancy is limited
• Reese et al. (NEJM, 2018) sought to determine the platelet counts in complicated and uncomplicated pregnancies to assess the occurrence and severity of thrombocytopenia throughout pregnancy

METHODS:

• Cohort Study (2011-2014)
• Participants
  • Women 15 to 44 years of age
• Platelet counts were compared with those of non-pregnant women
• Data on complications were also recorded, including those known to be associated with low platelet counts (e.g., HELLP and ITP)
• Twins were analyzed separately
  • Preterm defined as <37 weeks in singletons and <34 weeks in twins
• National Health and Nutrition Examination Survey (NHANES) data (nonpregnant women 15 to 44 years of age) were used for comparisons
• Primary objectives
  • Determine change in platelet counts during pregnancy
  • Determine whether rate of decrease differed during pregnancy between women with uncomplicated pregnancies compared to pregnancy-related complications/preexisting disorders
  • Recurrence risk

RESULTS:

• 7,351 provided sufficient data for the analyses
  • 4,568 had uncomplicated pregnancies
  • 2,586 had pregnancy-related complications
  • 197 had preexisting disorders associated with thrombocytopenia
• Mean platelet counts in uncomplicated pregnancies were as follows
  • First trimester (mean gestation, 8.7 weeks): 251,000 per cubic millimeter
  • Second trimester (mean gestation, 22.0 weeks): 230,000 per cubic millimeter
  • Third trimester (mean gestation, 32.1 weeks): 225,000 per cubic millimeter
  • Delivery (mean gestation, 39.0 weeks): 217,000 per cubic millimeter
  • Postpartum period (mean time after delivery, 7.1 weeks): 264,000 per cubic millimeter
• Uncomplicated pregnancies had lower platelet counts throughout pregnancy during each trimester and at delivery compared to nonpregnant women (P<0.001)
  • There was no difference in the postpartum period (P=0.10)
• At delivery
  • 9.9% of uncomplicated pregnancies had a platelet count <150,000 per cubic millimeter
  • Platelet counts <150,000 per cubic millimeter were more common among women who had pregnancy-related complications (11.9%) than among women who had uncomplicated pregnancies (9.9%); P=0.01
• In uncomplicated pregnancies
  • only 1% had a platelet count <100,000 per cubic millimeter
  • Only 0.1% of women with platelet counts <80,000 per cubic millimeter (median 65,000) had no explanation for their thrombocytopenia
• In women with pregnancy-related complications
  • 2.3% of women had a platelet count <100,000 per cubic millimeter throughout pregnancy and/or delivery
  • 1.2% had a platelet count <80,000 per cubic millimeter throughout pregnancy and/or delivery
  • HELLP: 28.0% had a platelet count <80,000 per cubic millimeter (median, 61,000; range, 32,000 to 78,000)
• Risk of recurrence was 14.2 (95% CI, 8.9 to 22.6) times as high among women who had previously had a platelet count <150,000 per cubic millimeter

CONCLUSION:

• Mean platelet counts are lower in pregnancy throughout gestation starting in the first trimester
• Platelet counts of less <100,000 per cubic millimeter warrants further investigation

Learn More – Primary Sources:

Platelet Counts during Pregnancy

Related ObG Topics:

Gestational Thrombocytopenia – a Diagnosis of Exclusion

Acute Fatty Liver of Pregnancy: A True Obstetric Emergency