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Grand Rounds

How Do Maternal Age and Pregnancy History Affect Risk of Miscarriage?

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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

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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

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