Objective: To assess the relation between the indication for fetal blood sampling and pregnancy loss following the procedure.
Design: Retrospective study.
Setting: The tertiary referral Fetal Medicine Units at Guy's and University College Hospitals, London.
Subjects: Women undergoing diagnostic fetal blood sampling in four groups: (1) 94 having prenatal diagnosis with normal ultrasound findings; (2) 94 with a structural fetal abnormality; (3) 30 having fetal assessment and (4) 35 with non-immune hydrops.
Interventions: Freehand ultrasound guided fetal blood sampling from umbilical cord, intrahepatic vein or fetal heart.
Main outcome measures: Pregnancy losses were divided into those within 2 weeks and those 2 weeks after the procedure, obstetric accidents and neonatal deaths.
Results: The 253 patients had fetal blood sampled on 268 occasions. Fifty-one pregnancies were terminated. Overall, 51 of the remaining 202 desired continuing pregnancies were lost, of which 19 (9%) were lost within 2 weeks of the procedure. After exclusion of the pregnancies that were terminated, the procedure-related losses within 2 weeks of sampling were 1 in 76 (1%), 5 in 76 (7%), 4 in 29 (14%) and 9 in 36 (25%) in groups 1, 2, 3 and 4 respectively.
Conclusions: The risk of fetal blood sampling is increased in abnormal pregnancies, reflecting the underlying pathology and this must be taken into account when counselling patients before the procedure.