How Does a Surrogate Mother Get Pregnant

A surrogate mother becomes pregnant through in vitro fertilization (IVF) embryo transfer — a medical procedure in which a pre-created embryo is placed into the surrogate’s uterus using a thin catheter under ultrasound guidance. The surrogate does not conceive through sexual intercourse. The embryo is genetically unrelated to the surrogate; it is created from the intended parents’ egg and sperm or donor gametes. The surrogate prepares for the transfer through a hormone medication protocol lasting 3-5 weeks.

This article explains the complete medical process by which a gestational surrogate becomes pregnant, from initial medication through pregnancy confirmation.

Overview of the Process

In gestational surrogacy, the surrogate mother becomes pregnant through a carefully coordinated medical process that involves four stages: hormonal preparation of the surrogate’s uterine lining, creation or thawing of the embryo, transfer of the embryo into the surrogate’s uterus, and confirmation of pregnancy through blood testing and ultrasound.

The surrogate does not contribute any genetic material. The embryo is created from the intended parents’ own eggs and sperm, or from donor eggs and/or donor sperm, depending on the intended parents’ medical circumstances and preferences.

This distinction is fundamental to gestational surrogacy and differentiates it from traditional surrogacy (in which the surrogate uses her own egg and is the genetic mother of the child). Traditional surrogacy is rarely practiced in the United States in 2026 due to the legal and emotional complexities it introduces.

Stage 1: Hormonal Preparation

Before an embryo can be transferred, the surrogate’s uterine lining must be prepared to receive and support the embryo. This is accomplished through a hormone medication protocol overseen by the fertility clinic.

Estrogen: The surrogate begins taking estrogen (typically estradiol valerate) to build and thicken the uterine lining (endometrium). Estrogen is administered via oral tablets, transdermal patches, or intramuscular injections, depending on the clinic’s protocol. The estrogen phase lasts approximately 2-3 weeks.

During the estrogen phase, the fertility clinic monitors the surrogate’s uterine lining thickness via transvaginal ultrasound. The target lining thickness is typically 8 millimeters or greater, with a trilaminar (three-layer) pattern indicating optimal receptivity.

Progesterone: Once the uterine lining reaches adequate thickness, the surrogate begins progesterone supplementation. Progesterone transforms the uterine lining from a proliferative state to a secretory state — the phase necessary for embryo implantation and early pregnancy support.

Progesterone is administered via intramuscular injection (progesterone in oil), vaginal suppositories, or a combination of both. Intramuscular progesterone injections are the most common method and are self-administered by the surrogate or administered by her partner. The injections use a 1.5-inch needle inserted into the upper outer quadrant of the buttock. Most surrogates describe the injections as uncomfortable but manageable, with injection site soreness being the most common side effect.

The progesterone phase begins approximately 5 days before the scheduled embryo transfer and continues for 10-12 weeks after pregnancy confirmation (through the first trimester), at which point the placenta produces sufficient progesterone to sustain the pregnancy independently.

Additional medications: Some protocols include additional medications such as low-dose aspirin (to promote uterine blood flow), antibiotics (to prevent infection around the transfer), methylprednisolone (a mild immune suppressant), or leuprolide (Lupron) to suppress the surrogate’s natural menstrual cycle before beginning the estrogen protocol.

Stage 2: Embryo Creation or Thawing

If the intended parents have existing frozen embryos: The embryos are thawed on the day of or the day before the scheduled transfer. Embryo thawing is a laboratory procedure with a survival rate of approximately 95% for embryos frozen using vitrification (the current standard freezing method).

If the intended parents need to create embryos: The intended mother or egg donor undergoes ovarian stimulation (2 weeks of injectable fertility medications), followed by egg retrieval (a 15-20 minute outpatient procedure). The retrieved eggs are fertilized with the intended father’s sperm or donor sperm in the laboratory. The resulting embryos are cultured for 5-6 days to the blastocyst stage, optionally biopsied for preimplantation genetic testing (PGT), and then frozen (vitrified) for future transfer.

Embryo creation and the surrogate’s uterine preparation may occur simultaneously or sequentially, depending on the intended parents’ timeline and the clinic’s protocol.

Stage 3: Embryo Transfer

The embryo transfer is a brief outpatient procedure performed at the fertility clinic. The procedure typically takes 10-15 minutes and does not require anesthesia.

Preparation: The surrogate arrives at the clinic with a moderately full bladder, which improves ultrasound visualization of the uterus. She changes into a hospital gown and is positioned on the procedure table.

The transfer: The reproductive endocrinologist (fertility specialist) inserts a speculum to visualize the cervix. A soft, thin catheter is loaded with the embryo by the embryologist in the adjacent laboratory. The catheter is guided through the cervical canal into the uterine cavity. The embryo is deposited at the optimal location within the uterus, guided by transabdominal ultrasound imaging. The catheter is then withdrawn and examined by the embryologist to confirm the embryo was successfully deposited.

After the transfer: The surrogate rests at the clinic for 15-30 minutes. She is then discharged with instructions to take it easy for 24-48 hours — avoiding strenuous activity, heavy lifting, and vigorous exercise. Normal daily activities can typically be resumed within 1-2 days.

In modern surrogacy practice, a single embryo transfer is standard. This reduces the risk of multiple pregnancy (twins or higher-order multiples). In rare cases, two embryos may be transferred with the consent of all parties, though this practice has become less common due to improved single-embryo success rates.

Stage 4: Pregnancy Confirmation

Beta-hCG blood test: Approximately 9-11 days after embryo transfer, the surrogate has a blood test measuring human chorionic gonadotropin (beta-hCG), the hormone produced by a developing embryo. A positive result (beta-hCG above a threshold level, typically >25 mIU/mL) indicates pregnancy.

A second beta-hCG test is performed 2-3 days later to confirm that hCG levels are rising appropriately (doubling approximately every 48-72 hours in early pregnancy).

Ultrasound confirmation: At approximately 6-7 weeks after embryo transfer, the surrogate undergoes a transvaginal ultrasound to confirm a gestational sac, fetal pole, and heartbeat. Confirmation of a heartbeat is typically the milestone at which the surrogate’s monthly compensation payments begin.

Transfer to OB care: After heartbeat confirmation (usually around 8-10 weeks), the surrogate is released from the fertility clinic’s care and transferred to her regular obstetrician for standard prenatal care throughout the remainder of the pregnancy.

Success Rates

The success rate for a single frozen embryo transfer in gestational surrogacy ranges from 50% to 65% per transfer attempt, depending on the quality of the embryo, the surrogate’s uterine receptivity, the clinic’s transfer technique, and whether the embryo was genetically tested (PGT-tested embryos have higher implantation rates).

If the first transfer is unsuccessful, a second transfer can typically be attempted after 1-2 menstrual cycles. Most surrogacy contracts allow for 2-3 transfer attempts. The cumulative success rate across multiple attempts exceeds 80% for most patients.

Frequently Asked Questions

Does the surrogate have to have sex to get pregnant?

No. The surrogate becomes pregnant through IVF embryo transfer, which is a medical procedure performed at a fertility clinic. There is no sexual contact involved in gestational surrogacy.

Is the embryo transfer painful?

Most surrogates describe the transfer as mildly uncomfortable but not painful — similar to a Pap smear. No anesthesia is required. Some women experience mild cramping during or after the procedure.

How long does the surrogate take hormones?

The hormone protocol begins 3-5 weeks before embryo transfer and continues through approximately 10-12 weeks of pregnancy (the end of the first trimester). The total medication period is approximately 13-17 weeks.

What happens if the transfer fails?

If the first transfer does not result in pregnancy, the surrogate and intended parents may proceed with a second or third attempt per the terms of their contract. The surrogate receives the transfer fee for each attempt regardless of outcome.