What an IVF pregnancy carries, once twins are taken out
Most of the crude difference is multiples. The rest is real and mostly about the placenta.
Assisted reproduction babies as a group do worse than other babies. Most of that gap is twins. Here it is both ways, from the 2018 national surveillance report:
| Outcome, 2018 surveillance | All ART infants | ART singletons only | All US infants |
|---|---|---|---|
| Born before 37 weeks | 26.1% | 14.9% | 10.0% (8.3% for singletons) |
| Low birth weight | 18.3% | 8.3% | 8.3% (6.6% for singletons) |
Restricting to single babies cuts the preterm gap from about 16 percentage points to about 6.6, and the low birth weight gap from about 10 points to about 1.7.
An earlier topic in this part quotes a lower figure, 12.5% preterm. Two things separate them. The 12.5% is from the 2022 data, four years later, and practice kept changing across those years: single embryo transfer rose from 71.0% to 85.9% of transfers and twins fell from 18.1% to 8.4% of ART infants, the tail of a longer shift that began at 30.8% and 38.1% in 2013. The 12.5% also counts a narrower group, a single baby from a pregnancy that was single from the start, while the 14.9% counts all ART single babies.
What remains is not nothing. Pooling 50 cohort studies covering 161,370 IVF singleton pregnancies against 2.28 million spontaneous ones:
| Outcome in IVF singletons | Relative risk (95% CI) |
|---|---|
| Placenta previa | 3.71 (2.67 to 5.16) |
| Antepartum haemorrhage | 2.11 (1.86 to 2.38) |
| Placental abruption | 1.83 (1.49 to 2.24) |
| Preterm birth | 1.71 (1.59 to 1.83) |
| Low birth weight | 1.61 (1.49 to 1.75) |
| Cesarean delivery | 1.58 (1.48 to 1.70) |
| Gestational diabetes | 1.31 (1.13 to 1.53) |
| Pregnancy-induced hypertension | 1.30 (1.04 to 1.62) |
Also, part of the early birth is a decision rather than spontaneous labor. Medically indicated preterm birth before 37 weeks ran at 4.73% after IVF against 1.81% after spontaneous conception, odds ratio 2.47 (95% CI 1.46 to 4.18).
The practical consequence is that an IVF pregnancy is watched more closely, and that placental problems are the specific thing being watched for. That is a reasonable use of extra surveillance, and it is worth knowing why the extra scans are happening.