BACKGROUND AND PURPOSE:

• Multiple factors have been associated with increased miscarriage risk including
  •  Parental age | Genetics |Hormonal | Immunologic | Environmental
  • Maternal age is the strongest known risk factor
• Magnus et al (The BMJ, 2019) sought to
  • Estimate the burden of miscarriage in the Norwegian population
  • Evaluate whether pregnancy history may also play  role in miscarriage

METHODS:

• Prospective register-based study (2009-2013)
  • Participants: Norwegian women
  • Register includes not only birth registry data but also a patient register that provides information on all patient-specialist contact so early losses would also be detected in this system
• Primary outcome: risk of miscarriage (losses between 6 and 20 weeks) based on
  • Maternal age
  • Pregnancy history categorized as
    • No previous pregnancy | Live birth | Stillbirth | Miscarriage | Neonatal death (defined as death within 28 days following delivery)
  • Information also obtained on adverse perinatal complications in the previous live birth pregnancy (e.g., preterm birth, preeclampsia)
• Statistical analysis: Risk estimates using logistic regression

RESULTS:

• 421,201 pregnancies

Maternal age as a risk factor – ‘J shaped pattern’

• Overall lowest risk group: 25-29 years (9.8%)
  • Absolute lowest risk: Age 27 (9.5%)
• High risk groups included oldest and highest in age
  • Highest risk group: ≥45 years (53%)
  • Youngest mothers: <20 years (15.8%)
  • Risk rose rapidly >age 30
• No real change when induced abortions were factored in

Pregnancy history as a risk factor

• Strong risk of miscarriage if prior miscarriage history is present (compared with the risk of miscarriage in women having their first pregnancy)
  • 1 miscarriage: Adjusted odds ratio (aOR) 1.54 (95% CI, 1.48 to 1.60)
  • 2 consecutive miscarriages: aOR 2.21 (95% CI, 2.03 to 2.41)
  • 3 consecutive miscarriages: aOR 3.97 (95% CI, 3.29 to 4.78)
• Risk of miscarriage increased if previous birth ended in
  • Preterm birth: aOR 1.22, (95% CI, 1.12 to 1.29)
  • Stillbirth: aOR 1.30 (95% CI, 1.11 to 1.53)
  • Cesarean section: aOR 1.16 (95% CI 1.12 to 1.21)
• Increased risk also seen in the following
  • Prior GDM: aOR 1.19 (95% CI, 1.05 to 1.36)
  • Women had been SGA themselves: aOR 1.08 (95% CI, 1.04 to 1.13)

CONCLUSION:

• Maternal age risk for miscarriage follows a ‘J shaped’ curve
• Other pregnancy complications may share underlying mechanisms resulting in associations with miscarriage risk
• Relationship to cesarean section is unclear and may reflect that a similar issue giving rise to the need for a cesarean section is the same as that for the subsequent miscarriage (i.e. not causal)

Learn more – Primary Sources:

Role of maternal age and pregnancy history in risk of miscarriage: prospective register based study

Related ObG Topics:

Maternal Age: What is the Impact on Stillbirth and Other Adverse Pregnancy Outcomes?

Maternal Age 45 and Over – What is the Impact on Maternal and Newborn Health?

Benefit or Risk to Delaying Pregnancy after Miscarriage?

How Effective are Treatments for Unexplained Recurrent Miscarriage?

Managing Early Pregnancy Loss