The hormone most responsible for early pregnancy symptoms, hCG, peaks between weeks 9 and 14 of gestation, then drops and stabilizes for the rest of pregnancy. But hCG is just one of several hormones at work. Estrogen and progesterone follow a completely different pattern, rising steadily until delivery. Understanding which hormone peaks when can help you make sense of how your body feels at each stage.
hCG: The First Trimester Hormone
Human chorionic gonadotropin, or hCG, is the hormone detected by pregnancy tests and the one most closely tied to early pregnancy symptoms. It rises rapidly in the first weeks after conception, doubling roughly every 48 to 72 hours. Levels reach their highest point around weeks 9 and 10, with a typical median concentration near 75,000 mIU/mL, though the normal range is wide. Some women measure as low as 16,000 and others above 160,000 at the same gestational age.
After peaking, hCG declines steadily and stabilizes at around 20,000 IU/L by weeks 14 to 16. This drop corresponds to the “luteal-placental shift,” when the placenta takes over hormone production from the corpus luteum (the temporary structure on the ovary that sustained the pregnancy in its earliest weeks). Once the placenta is fully in charge, hCG’s job is largely done, and levels stay relatively flat through delivery.
Why Nausea Peaks When hCG Does
Morning sickness tracks closely with hCG levels, which is why nausea tends to be worst between weeks 10 and 16. Women with conditions that produce higher-than-normal hCG, like molar pregnancies or carrying multiples, often experience more severe nausea. Studies have found that women with nausea and vomiting have measurably higher hCG levels in both blood and urine compared to women without symptoms.
For most women, nausea improves significantly after week 16 and resolves by week 20, following hCG’s decline. If you’re in the thick of it at weeks 8 through 12, the worst is likely close to its peak or already there.
Estrogen and Progesterone Rise Until Delivery
Unlike hCG, estrogen and progesterone don’t peak and fall during pregnancy. They climb continuously from early pregnancy all the way to delivery. Estradiol, the primary form of estrogen during pregnancy, reaches concentrations 100 times higher than pre-pregnancy levels by the third trimester. Progesterone follows a similar steady upward curve.
These two hormones are responsible for many of the changes you feel throughout pregnancy: breast tenderness, increased blood flow, mood shifts, and the gradual preparation of your body for labor and breastfeeding. Because they keep rising, some of the symptoms they drive (like swelling, heartburn, and fatigue) tend to intensify in the third trimester rather than easing up the way nausea does.
Relaxin Has Two Peaks
Relaxin is unusual among pregnancy hormones because it peaks twice. The first peak happens around weeks 12 to 14, at the end of the first trimester. Relaxin loosens ligaments and connective tissue, which is why joint pain and a feeling of “looseness” in your hips or pelvis can start surprisingly early. After that first peak, relaxin levels decline through the second and third trimesters.
The second surge comes just before delivery, when relaxin helps widen the cervix and relax the pelvis to prepare for birth. This late rise can bring back or worsen the pelvic instability and joint discomfort that some women noticed in the first trimester.
Placental Lactogen Peaks in Late Pregnancy
Human placental lactogen (hPL) is a hormone produced by the placenta that helps regulate your metabolism and direct nutrients toward the baby. It becomes detectable around 6 weeks after conception and rises gradually, reaching its highest levels around week 34. From there, it holds steady until delivery. Third-trimester concentrations typically range from 4.5 to 12.8 mcg/mL.
hPL is one of the hormones that makes your body more resistant to insulin in later pregnancy, which is part of why gestational diabetes screening happens in the second trimester. Your body becomes less efficient at processing sugar so that more glucose is available for the growing baby.
Oxytocin Builds Slowly, Then Surges at Birth
Oxytocin rises gradually from the first trimester through the third, but its most dramatic moment comes during labor. Levels increase at the onset of contractions and reach their highest point at the moment of delivery. After birth, oxytocin remains elevated to support breastfeeding and uterine contractions that help the uterus return to its normal size, then gradually decreases over the postpartum weeks.
How Twin Pregnancies Change the Timeline
Carrying multiples shifts the hormone picture in notable ways. At just 14 days post-conception, women carrying twins already show roughly double the hCG levels of singleton pregnancies (median of about 1,093 IU/L for twins versus 502 IU/L for singletons). Triplet pregnancies push levels even higher, with a median around 2,160 IU/L at the same early time point.
The hCG peak also arrives slightly later with multiples. In singleton pregnancies, hCG typically peaks between weeks 6 and 10 and then drops quickly. In twin pregnancies, the sustained rise lasts longer, with peak concentrations arriving around weeks 10 to 12 before declining into the second trimester. This extended, higher peak is one reason why nausea and vomiting tend to be more intense and last longer with twins.
A Week-by-Week Summary
- Weeks 4 to 8: hCG doubles rapidly. Early symptoms like fatigue, breast tenderness, and nausea begin.
- Weeks 9 to 10: hCG hits its median peak (around 75,000 mIU/mL). Nausea is often at or near its worst.
- Weeks 12 to 14: Relaxin reaches its first peak. hCG begins declining. The placenta takes over hormone production. Nausea starts improving for most women.
- Weeks 14 to 20: hCG stabilizes around 20,000 IU/L. Nausea typically resolves. Estrogen and progesterone continue climbing.
- Week 34: Placental lactogen plateaus at its highest level.
- Weeks 36 to 40: Estrogen and progesterone reach their pregnancy-long peaks. Oxytocin builds. Relaxin surges again just before labor.
- Delivery: Oxytocin spikes to its highest concentration as the baby is born.