01What the insert closes in early pregnancy
In patients with trichomoniasis, Flagyl tablets are contraindicated during the first trimester. Dosage text repeats: pregnant patients should not be treated during the first trimester.
That is a Flagyl line for T. vaginalis, not a home pregnancy test you run after you already started 250 mg. If pregnancy is possible, say so before the first swallow.
02What is known about fetal exposure
Metronidazole crosses the placental barrier. Effects on human fetal organogenesis are not known. Rat, rabbit, and mouse studies at doses similar to the maximum human dose (body-surface comparison) did not show fetal harm.
A 2 g day produces higher serum levels that can reach fetal circulation. That is why the one-day regimen is barred when a pregnant patient is treated after other options have been inadequate.
03What three infant-cancer studies could not settle
Three studies looked at infant cancer after metronidazole in pregnancy and did not show an increased risk. The insert says those studies had limited ability to detect such a signal.
That sentence is not a green light for a first-trimester trichomoniasis course. The contraindication remains.
04What the large pregnancy series showed
Case-control work, cohorts, and two meta-analyses cover more than 5,000 pregnant women who used metronidazole. Many of those exposures were in the first trimester.
One study reported more cleft lip, with or without cleft palate. Those findings were not confirmed. More than ten randomized, placebo-controlled trials enrolled more than 5,000 pregnant women to test antibiotic treatment (including metronidazole) for bacterial vaginosis and preterm delivery. Most studies did not show more congenital anomalies or other adverse fetal outcomes.
05If treatment happens after the first trimester
When a clinician treats a pregnant patient and alternatives have been inadequate, skip the one-day 2 g plan. Use a multi-day row they write, not a home 2 g stack of 250 mg tablets.
Partner treatment still applies for trichomoniasis. A partner who may be pregnant needs their own visit, not half of someone else's bottle. The partner probe is that job.
06What to say before the first 250 mg
If a period is late or a test might be positive, say so before the first Flagyl swallow. First-trimester trichomoniasis is already closed. Starting and then testing is the wrong order.
A partner who may be pregnant needs their own visit, not half of a seven-day bottle. Sharing under-doses both people and skips the gestational-age screen.