Clomid Success Rate: Ovulation, Pregnancy and Live Birth Are Three Different Numbers

The Clomid success rate quoted online is usually one number, and it is usually the wrong one for the question being asked. There are three: how many women ovulate on the drug, how many conceive, and how many take a baby home. Each is lower than the one before, each depends on why the woman was not ovulating, and the gap between them is where most disappointment with Clomid comes from. The label reports pregnancy in approximately 30% of the 7,578 women in the original trials; the two large randomised trials in polycystic ovary syndrome report live birth at 19 to 23% over five to six cycles; and the American Society for Reproductive Medicine's figures put ovulation at about 8 in 10 women with a per-cycle pregnancy chance of roughly 15 in 100 for those who respond.

This page sets the three numbers side by side, by source and by diagnosis, and then explains what moves them: age, the reason for anovulation, how many cycles are tried, and whether anything other than ovulation is wrong.

The ASRM figures are per cycle and per responder; the trial figures are cumulative over the whole study; the label figure is across all treatment. They are not in conflict, they are measuring different things, and a woman choosing Clomid needs the per-cycle number to set expectations and the cumulative number to decide how many cycles to give it.

Clomid's job is to make an egg release, and it does that in about four women in five with ovulatory dysfunction, most after the first course according to the label. The exceptions are predictable: women with very low estrogen (hypothalamic amenorrhoea) respond poorly because the drug works by blocking estrogen feedback that is not there; women with ovarian failure do not respond at all, and the label says Clomid cannot substitute for treating those causes. In PCOS, the largest group treated, the 2014 trial's cycle-by-cycle ovulation rate was 48%, meaning roughly half of all cycles attempted were ovulatory, with letrozole at 62%. Obesity and higher androgen levels lower the response. The signs Clomid is working guide covers how ovulation is confirmed.

Once ovulation happens, Clomid has done what it can, and the chance of conception in that cycle is governed by the same things as a natural cycle: the woman's age, egg quality, tubal patency, the partner's semen, and timing. That is why the per-cycle pregnancy rate in responders, about 15%, is no higher than a fertile couple's monthly chance, and why the label and ASRM both set a limit: the label says further treatment is not recommended after three ovulatory responses without pregnancy, and not recommended beyond about six cycles in total. Clomid is also known to thin the endometrium and cervical mucus in some women through its anti-estrogen action, which is one reason letrozole produced more live births for the same or fewer ovulations.

Live birth is pregnancy minus loss. In the 2014 trial, pregnancy loss was 29% on Clomid and 32% on letrozole, so roughly three in ten pregnancies in that PCOS population did not continue, which took a conception rate in the high twenties down to a 19% live-birth rate. In the label's trial data, of 2,369 pregnancies with known outcome, 483 ended in spontaneous abortion and 24 in stillbirth. Multiple pregnancy, 7.98% in the label, lowers infant survival further and is set out in Clomid and twins. Live birth is the number clinics are increasingly judged on, and it is the number by which letrozole beat Clomid in PCOS.

Age moves them most: the per-cycle chance falls through the thirties for every method, Clomid included. Diagnosis is next: unexplained infertility, where ovulation was never the problem, gets only 3 to 8 pregnancies per 100 cycles from Clomid alone in the ASRM figures, and about 9 with intrauterine insemination added, which is why Clomid for unexplained infertility is a weak choice. Weight matters in PCOS, where response falls as BMI rises. And the number of cycles matters up to a point: most pregnancies on Clomid occur in the first three to four ovulatory cycles, and the label's six-cycle ceiling exists because the yield after that is low and the ovarian-cancer question in prolonged use has never been fully resolved. When Clomid has had its chance, the next options are compared in Clomid alternatives.

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