spontaneous abortion

Last edited 09/2023 and last reviewed 09/2023

Miscarriage (previously known as spontaneous abortion) describes the spontaneous discharge of the gestational sac before the fetus is viable. Previously this applied to foetal loss up to 28 weeks gestation but since October 1992, it applies to losses up to 24 weeks. Spontaneous abortion is the process described by the lay public as miscarriage.

Miscarriages occur in up to 10-20% of clinical pregnancies (1). Majority is seen before the thirteenth week (2).

Most of the pregnancies end up as miscarriages even before a woman recognizes that she is pregnant since signs of miscarriage such as bleeding (usually with some abdominal pain and cramping) is mistakenly regarded as heavy or late menses (3).

• serial measurements of serum beta human chorionic gonadotropin in women who were unaware that they were pregnant have shown that the actual miscarriage rate is around 31% (3).
• vast majority occur in the first 14 days following conception.
• after the first few days of conception, the rate of miscarriage reduces sharply until the twelfth week of gestation (4)

Increasing maternal age is associated with increased foetal loss.

NICE state with respect to threatened miscarriage:

• a woman with a confirmed intrauterine pregnancy with a fetal heartbeat who presents with vaginal bleeding, but has no history of previous miscarriage, should be advised that:
  • if her bleeding gets worse, or persists beyond 14 days, she should return for further assessment
  • if the bleeding stops, she should start or continue routine antenatal care
• vaginal micronised progesterone 400 mg twice daily should be offered to women with an intrauterine pregnancy confirmed by a scan, if they have vaginal bleeding and have previously had a miscarriage
• if a fetal heartbeat is confirmed, continue progesterone until 16 completed weeks of pregnancy.

Reference:

• (1) Royal College of Obstetricians and Gynaecologists (RCOG) 2006. The management of early pregnancy loss  
• (2) Condous G et al. The conservative management of early pregnancy complications: a review of the literature. Ultrasound in Obstetrics and Gynaecology 2003;22(4):420-430
• (3) Griebel CP et al. Management of spontaneous abortion. Am Fam Physician. 2005;72(7):1243-50
• (4) Hobbins JC. Obstetric Ultrasound: Artistry in Practice. Chapter 1 Early pregnancy loss
• (5) NICE (September 2023).Ectopic pregnancy and miscarriage: diagnosis and initial management