hCG Levels in Early Pregnancy: What a Quantitative Blood Test Shows Week by Week

Human chorionic gonadotropin is made by the cells that become the placenta, beginning around the time the embryo implants — six to twelve days after ovulation. A home urine test detects hCG above a fixed threshold (usually 20–25 mIU/mL) and answers yes or no. A quantitative serum test measures the actual concentration, is sensitive to about 1–5 mIU/mL, and can therefore confirm pregnancy a few days earlier, at roughly 7–10 days after conception.

The number matters because it changes predictably. In a normally developing pregnancy hCG rises fast in the first weeks, peaks around weeks 8–11, then falls and plateaus for the rest of pregnancy. Two measurements 48 hours apart show whether the level is climbing as expected — which is why clinicians almost always order the quantitative test in pairs when there is a question about how the pregnancy is progressing.

The ranges below are typical for a single pregnancy, counted from the first day of the last menstrual period (LMP). They are wide on purpose: a "low" number for one woman is normal for another, and implantation date alone shifts the curve by days.

Weeks from LMP	Typical hCG range (mIU/mL)
3 weeks	5 – 50
4 weeks	5 – 426
5 weeks	18 – 7,340
6 weeks	1,080 – 56,500
7 – 8 weeks	7,650 – 229,000
9 – 12 weeks	25,700 – 288,000
13 – 16 weeks	13,300 – 254,000
17 – 24 weeks	4,060 – 165,400
25 weeks to term	3,640 – 117,000
Not pregnant	below 5

Because the ranges overlap so much, a single hCG value cannot date a pregnancy. Dating is done by LMP and, from about six weeks, by ultrasound. Twins and higher-order pregnancies usually run higher, but hCG alone does not diagnose them either.

The classic rule is doubling every 48–72 hours during the first four weeks after implantation, slowing to every 96 hours as the level passes about 6,000 mIU/mL. More recent data are less strict: in viable pregnancies the minimum 48-hour rise is around 35% when the starting level is under 1,500, about 40% from 1,500–3,000, and roughly 50% above 3,000 — so a level that goes from 400 to 620 in two days is within normal even though it did not double.

Once hCG is above about 1,500–2,000 mIU/mL, a transvaginal ultrasound should be able to see a gestational sac; this "discriminatory zone" is why a clinician who sees a high hCG with an empty uterus on ultrasound will look carefully for an ectopic pregnancy. Below the zone, ultrasound is often inconclusive and the paired blood tests do the work.

A rise slower than the minimums above, a plateau, or a fall can indicate a pregnancy that is not developing normally — an early loss or an ectopic pregnancy — but no single pattern is diagnostic. About a third of ectopic pregnancies show a "normal" rise, and some healthy pregnancies start slowly. Clinicians combine the trend with symptoms (one-sided pelvic pain, shoulder-tip pain, dizziness, bleeding), the ultrasound, and sometimes progesterone before drawing conclusions.

After an early loss, hCG falls and typically returns below 5 mIU/mL within two to six weeks depending on how high it was; a level that stops falling is a reason to be seen, because retained tissue or a molar pregnancy can keep it elevated. After delivery it is undetectable within about four weeks.

Same-day care is warranted for severe or one-sided abdominal pain, heavy bleeding, fainting or shoulder pain in early pregnancy regardless of the hCG number.

Occasionally. Fertility medications that contain hCG (the "trigger shot") stay detectable for up to about 10–14 days. Certain tumours — gestational trophoblastic disease, some germ-cell tumours of the ovary or testis — produce hCG, which is why the same test is used as a tumour marker in men. Around menopause the pituitary can secrete small amounts, producing low positives in the 5–15 range. Very rarely, antibodies in the blood interfere with the assay ("phantom hCG"), which a lab can check by testing urine or diluting the sample. A positive result in a man or a postmenopausal woman should always be discussed with a clinician.