Doctors prescribe hCG injections during pregnancy primarily to help your body produce enough progesterone to sustain the pregnancy in its earliest weeks. hCG (human chorionic gonadotropin) is a hormone your body already makes naturally once an embryo implants, but in certain situations, your natural levels may not be sufficient. The injections essentially give your body a boost of the same hormone it needs to keep the pregnancy going until the placenta is mature enough to take over, typically around seven weeks.
What hCG Does in Early Pregnancy
After you conceive, the developing placental tissue starts releasing hCG into your bloodstream. This hormone’s main job is to keep the corpus luteum alive and working. The corpus luteum is a small structure on the ovary left behind after ovulation, and it acts as your pregnancy’s temporary hormone factory. It produces progesterone and estrogen, both of which are critical for maintaining the uterine lining where the embryo has implanted.
hCG works by binding to the same receptors that luteinizing hormone (LH) uses on the ovary, but it’s significantly more potent and stays in the bloodstream longer. When it reaches the corpus luteum, it activates enzymes that ramp up progesterone production. Without enough hCG signaling in these early weeks, the corpus luteum can break down prematurely, progesterone levels drop, and the pregnancy may not survive. By about week seven, the placenta produces enough hormones on its own that the corpus luteum is no longer needed.
After IVF or Fertility Treatment
The most common reason for hCG injections during early pregnancy is luteal phase support after IVF or similar assisted reproduction procedures. During IVF, the medications used to stimulate your ovaries create an unusual hormonal environment. Multiple follicles develop instead of one, which leads to high estrogen levels early on. Those elevated hormones suppress LH through a feedback loop in the brain, and without adequate LH, the corpus luteum doesn’t get the signal it needs to keep producing progesterone.
This is called premature luteolysis, and it’s a well-recognized consequence of controlled ovarian stimulation. To compensate, fertility specialists provide luteal phase support, which can take the form of progesterone supplements, hCG injections, or both. hCG works indirectly by stimulating the corpus luteum to make its own progesterone, rather than replacing the hormone directly. Some doctors prefer this approach because it also triggers estrogen production alongside progesterone, more closely mimicking what happens in a natural pregnancy. The support typically continues through the first trimester until the placenta can reliably sustain hormone production on its own.
Recurrent Miscarriage
Some doctors prescribe hCG injections for women who have experienced recurrent miscarriage, defined as the loss of three or more consecutive pregnancies. The logic is that if the corpus luteum isn’t producing enough progesterone, supplementing with hCG could shore up that weak link. This is most likely to be recommended when no other cause for the miscarriages has been found, meaning testing for chromosomal problems, immune disorders, uterine abnormalities, clotting conditions, and hormonal imbalances has come back normal.
The evidence here is less clear-cut than in the IVF setting. A Cochrane systematic review looking at hCG for preventing miscarriage in women with unexplained recurrent loss found limited data. One study showed no benefit for women with regular menstrual cycles, though a small subgroup of women with irregular cycles did see a modest reduction in miscarriage rates (25% in the hCG group compared to 30% in the placebo group). That’s a narrow difference in a small sample, so the overall picture is that hCG may help some women but is not a guaranteed solution. Your doctor may still recommend it when other options have been exhausted, particularly if there’s reason to suspect your progesterone levels are marginal.
Low Progesterone in Early Pregnancy
Outside of IVF and recurrent miscarriage, some doctors will suggest hCG injections when blood work shows progesterone levels that are lower than expected for the stage of pregnancy. Low progesterone can show up as spotting or bleeding in the first trimester, or it may be caught on routine blood work. Rather than giving progesterone directly (which is more common), hCG injections encourage the corpus luteum to increase its own output. This can be a consideration for women with irregular cycles or a history that suggests their ovaries may not sustain the corpus luteum as long as needed.
What the Injections Feel Like
hCG is given as a subcutaneous or intramuscular injection, depending on the formulation. Many women give themselves the shots at home after a quick lesson from their clinic. The most common side effects are mild: bloating, pelvic discomfort, and tenderness at the injection site. Some women experience nausea or breast tenderness, which can be hard to distinguish from normal early pregnancy symptoms.
The more serious risk is ovarian hyperstimulation syndrome (OHSS), which happens when the ovaries overreact to the hormone. Mild OHSS causes bloating and pelvic pain. Severe OHSS, which is uncommon (occurring in less than 1% of cases with recombinant hCG), can lead to rapid weight gain, difficulty breathing, severe abdominal swelling, and decreased urine output. This risk is highest in women who have recently undergone ovarian stimulation for fertility treatment, since they already have enlarged ovaries with multiple follicles. If you notice sudden swelling, significant weight gain over a day or two, or trouble breathing, that warrants immediate attention.
How hCG Injections Affect Pregnancy Tests
One practical detail worth knowing: if you’ve received an hCG injection, it will show up on pregnancy tests. The injected hormone takes roughly 5 to 14 days to clear from your system, depending on the dose. A blood or urine pregnancy test taken during that window can produce a false positive, or it can make it impossible to tell whether rising hCG levels reflect a healthy pregnancy or leftover injected hormone. Most fertility clinics schedule the first pregnancy blood test at least 10 to 14 days after the last hCG injection to avoid this overlap. If you’re testing at home, a positive result within that window isn’t reliable, and a negative result doesn’t necessarily mean the treatment failed.
Once the injected hCG has cleared, your doctor can track your natural hCG levels through serial blood draws. In a healthy early pregnancy, hCG roughly doubles every 48 to 72 hours. That doubling pattern is one of the first reassuring signs that things are progressing normally, which is another reason doctors are careful about timing tests around injections.