In plain words
Fetomaternal hemorrhage is when some of the baby's blood cells cross into the mother's bloodstream. It can happen during late pregnancy, during birth, or after a procedure or injury. Usually the amount is small. It matters because a mother whose blood type is Rh-negative can form antibodies against the baby's Rh-positive blood cells. This is one reason Rh status is tested early in pregnancy. Some mothers are offered a medicine after certain events to lower the chance of this. Your provider will tell you whether you need it and when. Bleeding, abdominal pain, or reduced fetal movement after a fall or injury call for prompt care.
The deeper version
Fetomaternal hemorrhage (FMH) is common in small volumes, and large events are rare. Kleihauer-Betke testing quantifies fetal red cells in maternal blood and guides the dose of needed. ACOG Practice Bulletin 181 (2017) on prevention of Rh D alloimmunization describes postpartum and event-based prophylaxis. Residual cases arise from missed prophylaxis after sensitizing events, from occult antepartum hemorrhage, and from non-D antibodies, and the field is shifting toward fetal RHD genotyping to target prophylaxis. Large FMH carries risk of fetal anemia, and its incidence in cohort studies varies with the test threshold used.
Where it comes up
- Rh factor and RhoGAMPregnancy: Your Body
- Placenta previa and other placenta findingsPregnancy: Your Body
- Prenatal tests and ultrasounds: what each one isPregnancy: Your Body
What mothers here say about fetomaternal hemorrhage
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Sources
- American College of Obstetricians and Gynecologists — Practice Bulletin 181: Prevention of Rh D alloimmunization, 2017
- Kleihauer E et al. — Quantitative determination of fetal hemoglobin in maternal blood, 1957