Advanced Maternal Age: What It Is and What You Should Know
Most of my patients are over age 35. I also see patients every single day who schedule an appointment just because they are 35, and this number has been drilled into our brains—but we often don't even know why.
So let's talk about why this number exists, what it really means for us, and how we can think about our fertility and our health in pregnancy as we age.
Why Age 35 Matters
This number was chosen due to two main reasons:
Fertility Rates Decrease: The definition of infertility includes this number. If you're under 35 and trying for 12 months without success, it's considered infertility. If you're over 35 and trying for 6 months, that's also considered infertility.
Increase in Genetic Abnormalities: There's an increase in chromosomal abnormalities and miscarriages as we age.
Your eggs are stored in a vault inside your ovaries from the moment you're born. These chromosomes are held in perfect suspension and don't divide until ovulation. Proteins keep these chromosomes in place, but over time—due to age, inflammation, environmental toxins, and lifestyle factors—these proteins degrade, increasing the chance of abnormalities.
By age 35, about half of the eggs are chromosomally normal and half are not. This is based on IVF and genetic testing data.
Health Risks with Advanced Maternal Age
As we age, medical problems like high blood pressure, cholesterol issues, thyroid disease, and diabetes become more prevalent. These can all impact pregnancy outcomes. ACOG (American College of OB/GYN) uses these risk factors to support the advanced maternal age (AMA) designation.
Natural Fertility Rates by Age
<30 years: 20-25% chance of pregnancy per month
34-35 years: 11-12%
38-39 years: 5%
42 years: 3%
These stats come from Anne Steiner's Time to Conceive study. If you've had a child before, your fertility rates are typically a bit higher.
AMA and Pregnancy Safety
Once you are 35 or older, your pregnancy is labeled "high-risk." This includes:
Higher chance of preeclampsia
Increased gestational diabetes
Increased risk of C-section
Risk of low birth weight and NICU admissions
More observation is not bad—these risks increase gradually, not suddenly at 35.
Recommendations for AMA Pregnancy
Low Dose Aspirin
If you're 35+ with one or more additional risk factors, start 81 mg of baby aspirin between 12-16 weeks. Risk factors include:
First-time mom
BMI >30
Family history of preeclampsia
African American
Lower socioeconomic status
History of preterm birth
Long interval between pregnancies
Known high blood pressure, twins, diabetes, kidney disease, or lupus
First Trimester Ultrasound
Even without fertility treatments, your body may ovulate more than one egg, increasing the risk of twins due to stronger FSH signals.
Genetic Screening
Do prenatal genetic screening (NIPT), possibly amniocentesis, and detailed anatomy scans. Most abnormal embryos do not implant or result in miscarriage. However, the risk of having a child with chromosomal abnormalities does increase with age:
Down Syndrome (Trisomy 21):
Age 20: 1 in 1,250
Age 30: 1 in 714
Age 40: 1 in 86
All Chromosome Abnormalities:
Age 20: 1 in 122
Age 30: 1 in 110
Age 40: 1 in 40
This is a major reason why IVF with genetic testing is increasingly recommended.
Monitoring and Delivery
Third Trimester Growth Ultrasound: Ask your provider about growth scans.
Stillbirth Risks:
General population: 6 in 1,000
Age 40: 10 in 1,000
Stillbirth risk increases even after controlling for blood pressure and diabetes. It also increases after 41 weeks:
35-40 years old at 41 weeks: Risk jumps to 6%
Over 40 at 41 weeks: Risk increases to 8%
So fetal surveillance starting at 32–36 weeks is usually recommended, especially after age 40.
Timing of Delivery
For women over 40, delivery is strongly recommended in the 39th week to avoid increasing stillbirth risk.
Final Thoughts
Most of my patients over 35 get pregnant and do great! But you need to advocate for your health. Know if you should be on baby aspirin, ask about monitoring, and stay informed. Taking care of your body is the most important thing you can do. Age 35 is not a hard cutoff—just a point where risk starts to climb.
Resources:
Pregnancy at Age 35 Years or Older: ACOG Obstetric Care Consensus No. 11. Obstetrics & Gynecology 140(2):p 348-366, August 2022. | DOI: 10.1097/AOG.0000000000004873
Steiner AZ, Jukic AM. Impact of female age and nulligravidity on fecundity in an older reproductive age cohort. Fertil Steril. 2016;105(6):1584–1588.
Steiner AZ, Pritchard D, Stanczyk FZ, et al. Association Between Biomarkers of Ovarian Reserve and Infertility Among Older Women of Reproductive Age. JAMA. 2017;318(14):1367–1376.
