# Toxoplasmosis in Pregnancy

> Toxoplasmosis in pregnancy for NEET-PG Obstetrics and Gynaecology, covering serology, spiramycin versus pyrimethamine regimens and fetal sequelae.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/toxoplasmosis-in-pregnancy
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Williams Obstetrics; Ananthanarayan and Paniker's Textbook of Microbiology; Dutta's Textbook of Obstetrics
- How to cite: "Toxoplasmosis in Pregnancy", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/toxoplasmosis-in-pregnancy

## Direct answer

Toxoplasmosis is infection with the protozoan Toxoplasma gondii, acquired from undercooked meat or cat faeces, and it can cross the placenta to infect the fetus. Serology distinguishes past from recent infection, and spiramycin is used to reduce transmission to the fetus. Pyrimethamine with sulfadiazine and folinic acid is reserved for confirmed fetal infection, because pyrimethamine is avoided in early pregnancy.

## What you must remember

- **Transmission:** Undercooked meat, unwashed produce, unpasteurised milk and contact with cat faeces or litter are the usual sources.
- **IgG and IgM:** Positive IgG alone suggests past infection; a new IgG with IgM, or a rising titre on paired samples, suggests recent infection.
- **IgG avidity:** Low avidity points to infection within roughly the previous few months, while high avidity makes recent infection unlikely.
- **Spiramycin:** Given to the mother after maternal infection to reduce placental transmission, until fetal infection is excluded.
- **Pyrimethamine and sulfadiazine:** Given with folinic acid for confirmed fetal infection, because pyrimethamine is a folate antagonist.
- **Congenital triad:** Hydrocephalus, intracranial calcification and chorioretinitis; sequelae include visual impairment, seizures and learning difficulty.
- **Amniotic fluid PCR:** Used for fetal diagnosis, generally after about 18 weeks and several weeks after maternal infection.

## Serology, spiramycin and fetal confirmation, step by step

Management hinges on whether the fetus is infected, which is established by amniotic fluid PCR and ultrasound rather than by maternal serology alone. The steps below set out the sequence.

1. **Confirm the serology:** Send IgG, IgM and IgG avidity to a reference laboratory, because in-house IgM assays give many false positives.
2. **Date the infection:** Work out when seroconversion occurred from paired samples and the history, since this decides the next step.
3. **Treat the mother:** Start spiramycin once maternal infection is established, to reduce transmission across the placenta.
4. **Test the fetus:** Amniocentesis for toxoplasma PCR is done after about 18 weeks and several weeks after maternal infection; ultrasound and fetal MRI add information.
5. **Switch for fetal infection:** Pyrimethamine with sulfadiazine and folinic acid is started once fetal infection is confirmed, with blood counts monitored.
6. **Follow the newborn:** Congenital infection is treated after birth for about a year, with ophthalmological and neurological follow-up.

## Where the examiner tries to catch you

Viva questions on toxoplasmosis focus on the serology logic and on drug choice according to fetal status.

- **Trap:** Reading a positive IgM as proof of recent infection — **Correct:** IgM can persist for months or give false results, so IgG avidity and paired sera are needed.
- **Trap:** Starting pyrimethamine in the first trimester for every infected woman — **Correct:** Pyrimethamine is avoided in early pregnancy, and spiramycin is used while fetal infection is excluded.
- **Trap:** Treating an infected pregnant woman without testing the amniotic fluid — **Correct:** Fetal infection is confirmed by PCR, and that result decides whether the stronger regimen is started.

## Frequently asked questions

### Which serology pattern suggests recent toxoplasmosis in pregnancy?

Recent toxoplasmosis is suggested by a newly positive or rising IgG with IgM, together with low IgG avidity on testing. Paired samples taken several weeks apart are used to confirm seroconversion.

### Why is spiramycin used in pregnant women with toxoplasmosis?

Spiramycin is used in pregnant women with toxoplasmosis to reduce transmission across the placenta while fetal infection is being excluded. It is a macrolide and is preferred in early pregnancy because pyrimethamine is avoided there.

### When is pyrimethamine with sulfadiazine started in toxoplasmosis?

Pyrimethamine with sulfadiazine and folinic acid is started when fetal infection is confirmed, usually by amniotic fluid PCR or characteristic ultrasound findings. Pyrimethamine is avoided in the first trimester because it is a folate antagonist with teratogenic concern.

### What fetal sequelae follow congenital toxoplasmosis?

Congenital toxoplasmosis causes hydrocephalus, intracranial calcification and chorioretinitis, with possible visual impairment, seizures and learning difficulty. Late-onset retinochoroiditis may appear in childhood, so follow-up continues after birth.