Modes of conception and multiple pregnancy: a national survey of babies born during one week in 2003 in the United Kingdom.

OBJECTIVE: To collect data on every baby born in one week in the United Kingdom with respect to mode of conception, multiplicity of pregnancy, and outcome.

DESIGN: A questionnaire completed by the midwife birth attendant.

SETTING: All maternity units in the United Kingdom.

PATIENT(S): All mothers delivering during the week of April 6-12, 2003.

INTERVENTION(S): Questionnaire survey.

MAIN OUTCOME MEASURE(S): Mode of conception (both spontaneous and assisted), type of fertility treatment, multiplicity of pregnancy, mode of delivery, gestational age, and fetal outcome.

RESULT(S): Data were received from 178 maternity units (72.7%) on 6,913 deliveries: 6,812 (98.54%) were singleton, 100 (1.45%) twin, and 1 (0.01%) triplet. In total, 7,015 babies were born. Of all pregnancies, 6,638 (96%) (including the only triplet) were conceived spontaneously and 133 (1.9%) with assistance. The multiple pregnancy rate was significantly greater in assisted (13.5%) than in spontaneous (1.2%) conceptions. Of the multiple pregnancies after fertility treatment, 16.7% resulted from clomifene citrate therapy, 72.2% from IVF or frozen embryo replacements (FET), and 5.6% from superovulation with intrauterine insemination (IUI). The multiple pregnancy rate after IVF/FET (26%) was significantly higher than the one after clomifene citrate therapy (7.3%). In total, 41 babies were born after clomifene citrate therapy, 50 after IVF/ET, and eight after superovulation IUI. The live birth rate was higher for singleton (98.2%) than multiple pregnancies (93.6%).

CONCLUSION(S): Multiple pregnancy from IVF and related treatments remains a significant problem and contributes a greater burden than ovulation induction therapies.