Pregnancy
What is pregnancy?
Pregnancy is the period during which a developing embryo, and later a fetus, grows inside a woman’s uterus. It begins when a fertilized egg implants in the lining of the uterus and ends with birth, miscarriage, or termination. A typical pregnancy lasts about 40 weeks (280 days), counted from the first day of the last menstrual period, and is divided into three trimesters.
The medical definition
The international fertility glossary used by the World Health Organization and the American Society for Reproductive Medicine (ASRM) defines pregnancy as starting at implantation rather than at fertilization, and ending when the pregnancy is fully delivered or otherwise ends.
In a gestational surrogacy, the embryo is created in a lab from the intended parents’ or donors’ egg and sperm, then transferred to the surrogate’s uterus. The surrogate becomes pregnant only if that embryo implants. She carries the pregnancy, but she is not genetically related to the baby.
Why “when pregnancy begins” matters more in surrogacy
In an unassisted pregnancy, fertilization and implantation both happen inside the body, a few days apart, and nobody can see either one. In surrogacy, they are separated by days, months, or years. An embryo can be created in a lab and frozen long before it is transferred to the surrogate. The American College of Obstetricians and Gynecologists (ACOG) has defined pregnancy as starting at implantation since 1965, and one reason doctors point to is exactly this: IVF makes it possible to have fertilization without a pregnancy.
That’s why a frozen embryo in storage is not a pregnancy, and why a surrogate is not pregnant until after transfer and implantation.
A note on legal definitions. Medical definitions and legal definitions don’t always match. Some state laws define pregnancy or “unborn child” as starting at fertilization. In February 2024, the Alabama Supreme Court ruled that frozen IVF embryos count as children under the state’s wrongful death law. Alabama’s legislature passed a law shielding IVF providers from liability less than three weeks later, but the court’s definition itself was left in place. If you’re considering surrogacy, the laws of your state (and the state where embryos are stored) can affect your contract. See our [state surrogacy laws] pages and talk to your own attorney.
The three clocks of a surrogate pregnancy
One of the most confusing parts of being a surrogate is that three different counts run at once.
- Gestational age is the count your OB uses. By convention, it starts about two weeks before conception, mimicking the first day of a last menstrual period. Pregnancy lasts about 40 weeks (280 days) on this clock.
- Embryo age is how old the embryo was when it was transferred, usually 5 days (a blastocyst) and sometimes 3 or 6 days.
- Days post transfer (DPT) is the count surrogates and clinics use in the early weeks, as in “5dp5dt.”
For IVF and surrogate pregnancies, ACOG says the due date should be calculated from the transfer date and the embryo’s age, not from a menstrual period. For a 5-day embryo, the due date is 261 days after transfer. For a 3-day embryo, it’s 263 days after transfer.
This leads to something that surprises a lot of first-time surrogates. On the day of a 5-day embryo transfer, your gestational age is already 2 weeks and 5 days, even though you aren’t pregnant yet.
Milestones on all three clocks (5-day embryo, frozen embryo transfer)
| Milestone | Days after transfer | Gestational age (OB count) |
|---|---|---|
| Embryo transfer | 0 | 2 weeks 5 days |
| Implantation begins | Usually within the first few days | About 3 weeks |
| First beta hCG blood test | About 9–10 | About 4 weeks |
| First ultrasound (heartbeat check) | About 3–4 weeks | About 6–7 weeks |
| Release (“graduation”) from fertility clinic to OB | About 5–9 weeks | About 8–12 weeks |
| End of first trimester | 78 | 13 weeks 6 days |
| End of second trimester | 176 | 27 weeks 6 days |
| Full term begins | 254 | 39 weeks 0 days |
| Estimated due date | 261 | 40 weeks 0 days |
Clinic timing varies, especially for the beta, ultrasound, and release to OB. Follow your own clinic’s schedule.
Pregnancy stages and terms
Trimesters. The first trimester runs through 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days until birth.
Term categories. In 2013, ACOG and the Society for Maternal-Fetal Medicine replaced the single label “term” with four categories, because research showed newborn outcomes differ week by week:
| Category | Gestational age |
|---|---|
| Preterm | Before 37 weeks 0 days |
| Early term | 37 weeks 0 days – 38 weeks 6 days |
| Full term | 39 weeks 0 days – 40 weeks 6 days |
| Late term | 41 weeks 0 days – 41 weeks 6 days |
| Postterm | 42 weeks 0 days and beyond |
Outcomes are best for babies born at full term, which is why doctors generally avoid planned deliveries before 39 weeks unless there’s a medical reason.
Early pregnancy terms you’ll hear after transfer
- Biochemical pregnancy: A pregnancy detected only by an hCG blood or urine test, before anything can be seen on ultrasound. When people say “chemical pregnancy,” they usually mean one that ended at this stage.
- Clinical pregnancy: A pregnancy confirmed by ultrasound showing a gestational sac (or other definitive clinical signs). Fertility clinics report success rates using this measure.
- Clinical pregnancy with fetal heartbeat: An ultrasound shows at least one fetus with a heartbeat. For many surrogacy journeys, this is the milestone that triggers payments or the release to OB.
- Pregnancy of unknown location: A positive hCG test when ultrasound can’t yet show where the pregnancy is. Your clinic will usually monitor this with repeat tests.
Is a surrogate pregnancy riskier than a regular pregnancy?
Every pregnancy carries risk, and surrogates should hear the evidence plainly. Three of the largest recent studies point in a similar direction but don’t all agree.
| Study | What it looked at | Key findings |
|---|---|---|
| Velez et al., Annals of Internal Medicine, 2024 | Every singleton birth after 20 weeks in Ontario, Canada, 2012–2021, including 806 gestational carrier births | Severe maternal complications occurred in 7.8% of gestational carrier births, compared with 4.3% after IVF and 2.3% after unassisted conception. Gestational carriers also had more high blood pressure disorders, postpartum hemorrhage, and preterm birth. Severe complications in newborns were not clearly higher. |
| Masjedi et al., Journal of Assisted Reproduction and Genetics, 2024 | About 14.3 million U.S. hospital deliveries, 2017–2020 | Gestational carriers were more likely to carry multiples (14.7% vs. 1.8%) and had more placental abruption, low-lying placenta, and postpartum hemorrhage. They were less likely to have a C-section in singleton pregnancies (23.6% vs. 31.6%). |
| Systematic review and meta-analysis, JAMA Network Open, 2024 | Six studies covering about 28,300 gestational carrier pregnancies | Gestational carriers had higher odds of high blood pressure disorders than the general pregnant population, but similar rates of preterm birth and low birth weight compared with other IVF pregnancies. Severe complications and maternal deaths were rare. |
What this means in practice
- Most surrogate pregnancies go well, but the risk of certain complications, especially high blood pressure disorders and heavy bleeding after birth, appears higher than for an unassisted pregnancy. Researchers don’t yet know exactly why.
- Carrying more than one baby raises the risk significantly. ASRM considers single embryo transfer the preferred approach for surrogacy cycles for this reason.
- Screening matters. ASRM recommends that surrogates be between 21 and 45, ideally have had at least one full-term, uncomplicated pregnancy, and ideally have had no more than five previous deliveries or three C-sections. The lead author of the Ontario study noted that these guidelines aren’t always strictly followed.
- Ask about your care plan. Before transfer, ask your clinic and OB how they monitor blood pressure, what happens if you develop complications, and whether you’ll have access to a maternal-fetal medicine (high-risk pregnancy) specialist.
Whose pregnancy is it?
The baby belongs to the intended parents, but the pregnancy happens in the surrogate’s body. ASRM’s guidance recognizes that the surrogate keeps her bodily autonomy and the authority to make medical decisions throughout the pregnancy. Your surrogacy agreement will cover topics like prenatal testing, delivery plans, and the number of embryos transferred, and you should have your own independent attorney review it before you sign.
Related terms
Embryo Transfer (ET) · Frozen Embryo Transfer (FET) · Gestational Carrier · Multiple Gestation Pregnancy · Selective Reduction · Parentage Order · Surrogate Medical Insurance
Sources
- Zegers-Hochschild F, et al. The International Glossary on Infertility and Fertility Care, 2017. Fertility and Sterility / Human Reproduction. https://www.asrm.org/practice-guidance/practice-committee-documents/the-international-glossary-on-infertility-and-fertility-care-2017-2017/
- ACOG Committee Opinion No. 700: Methods for Estimating the Due Date. Obstet Gynecol 2017;129:e150–4. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date
- ACOG Committee Opinion No. 579: Definition of Term Pregnancy. Obstet Gynecol 2013. https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/11/definition-of-term-pregnancy
- Velez MP, et al. Severe Maternal and Neonatal Morbidity Among Gestational Carriers: A Cohort Study. Ann Intern Med 2024;177:1482–1488 (correction published 2025). https://www.acpjournals.org/doi/10.7326/M24-0417
- Masjedi AD, et al. National-level assessment of gestational carrier pregnancies in the United States. J Assist Reprod Genet 2025;42(1):201–211. https://link.springer.com/article/10.1007/s10815-024-03320-5
- Obstetric Characteristics and Outcomes of Gestational Carrier Pregnancies: A Systematic Review and Meta-Analysis. JAMA Netw Open 2024. https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2821391
- ASRM Practice Committee. Recommendations for practices using gestational carriers: a committee opinion (2022). Fertil Steril 2022;118(1):65–74. https://www.asrm.org/practice-guidance/practice-committee-documents/recommendations-for-practices-using-gestational-carriers-a-committee-opinion-2022/
- ASRM. Just the Facts: Gestational Carrier Care in the United States. https://www.asrm.org/advocacy-and-policy/fact-sheets-and-one-pagers/just-the-facts-gestational-carrier-care-in-the-united-states/
- Chervenak et al. Obstetrician-gynecologists’ beliefs about when pregnancy begins. Am J Obstet Gynecol. https://www.ajog.org/article/S0002-9378(11)02223-X/fulltext
- LePage v. Center for Reproductive Medicine, P.C. (Ala. Feb. 16, 2024); ASU Center for Public Health Law and Policy memo, March 2024. https://law.asu.edu/sites/default/files/2024-07/ASU-CPHLP-Memo-Alabama-IVF-Case.pdf