Toxoplasma IgG negative and IgM positive in pregnancy

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CDC toxoplasmosis pregnancy positive IgM negative IgG confirmatory testing avidity

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toxoplasmosis pregnancy serology

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https://www.cdc.gov/dpdx/toxoplasmosis/index.html

Toxoplasma IgG negative + IgM positive in pregnancy is indeterminate. It does not prove a new infection.

Most commonly, this pattern is due to a false-positive IgM result. Less commonly, it can represent a very early infection, before IgG antibodies have appeared.

What to do promptly

Contact your obstetrician or maternal-fetal medicine specialist today or next working day.
Repeat Toxoplasma IgG and IgM in about 2 to 3 weeks, preferably through the same laboratory, and send the original and repeat samples for reference-laboratory confirmatory testing.
If IgG becomes positive or rises on repeat testing, that supports a recent infection. A reference lab may use a more detailed antibody panel. IgG avidity is useful only once IgG is detectable.
Do not start anti-toxoplasma treatment based on this one screening result alone. Management depends on whether recent maternal infection is confirmed and on gestational age.

Commercial Toxoplasma IgM tests have enough false-positive results that they should not be used alone to diagnose infection in pregnancy. Confirmation at a specialist reference laboratory is recommended. Medical Microbiology 9e, p. 823. The CDC diagnostic guidance similarly advises confirmatory testing when timing of infection is important in pregnancy.

Until clarified, use prevention measures: avoid undercooked meat, wash produce, wear gloves for soil/gardening, and avoid changing cat litter if possible. If you must do it, use gloves and wash hands well.

A recent systematic review also supports using combined repeat serology and additional assays rather than interpreting IgM alone (PMID 40329230).

Seek urgent assessment if you have fever, swollen neck glands, visual symptoms, or if your clinician believes you had a meaningful recent exposure.

How is toxoplasmosis confirmed when IgM is positive and IgG is negative?

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toxoplasmosis pregnancy serology

With IgM positive and IgG negative, toxoplasmosis is not confirmed by that initial result. It may be a false-positive IgM or a very early infection.

Confirmation is done by:

Repeat Toxoplasma IgG and IgM on a new blood sample after about 2 to 3 weeks.
- IgG seroconversion, meaning IgG changes from negative to positive, confirms a newly acquired infection.
- A significant rise in IgG titre in paired samples also supports acute infection.
Send the original and follow-up samples to a specialist/reference laboratory for confirmatory serology.
- They use a panel of more specific tests to verify whether IgM is truly Toxoplasma-specific and assess the pattern of recent versus older infection.
- A positive commercial screening IgM by itself is insufficient, particularly in pregnancy.
PCR for Toxoplasma DNA may confirm infection if there is an appropriate specimen and clinical indication.
- For suspected fetal infection, amniotic-fluid PCR is the preferred diagnostic test, after discussion with maternal-fetal medicine. It is not the first step for an isolated maternal IgM-positive/IgG-negative result.

IgG avidity cannot help yet because there is no measurable IgG. It can be considered only after IgG becomes positive.

The best evidence of a true recent maternal infection in this situation is therefore documented IgG seroconversion on serial samples, together with reference-lab confirmation. Creasy & Resnik’s Maternal-Fetal Medicine, p. 1219. The CDC 2024 case definition likewise recognizes seroconversion during pregnancy or a fourfold IgG rise in samples taken at least 3 weeks apart as confirmatory evidence.

Arrange this promptly through your obstetrician or maternal-fetal medicine specialist.

Increased Nuchal fold thickness at 22 weeks

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SMFM isolated thickened nuchal fold second trimester ultrasound 6 mm trisomy 21 recommendations

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nuchal fold thickness trisomy 21

At 22 weeks, an increased nuchal fold means extra thickness of soft tissue at the back of the fetal neck on the anatomy ultrasound. It is different from first-trimester nuchal translucency.

A nuchal fold of 6 mm or more is generally considered enlarged in the second trimester.
It is a soft marker, not a diagnosis. Its main association is with trisomy 21 (Down syndrome), but many fetuses with an isolated thickened nuchal fold do not have a chromosome condition.
It becomes more concerning if there are other ultrasound findings, a structural anomaly, or high-risk prior screening.

Next steps depend on what has already been done:

Situation	Usual discussion with obstetrician/MFM
No prior aneuploidy screening	Offer cell-free DNA screening (NIPT) or diagnostic testing with amniocentesis.
Low-risk cell-free DNA/NIPT and the fold is isolated	SMFM recommends no further aneuploidy evaluation is generally needed.
Low-risk serum screening, isolated thickened fold	Review the revised risk and consider NIPT or amniocentesis, depending on your preference.
Other markers or structural findings present	Detailed fetal assessment, genetic counseling, and usually offer amniocentesis with chromosome testing, often including microarray.

A detailed review of the anatomy scan is important, particularly the heart and other structures. Only diagnostic testing, usually amniocentesis with fetal chromosome analysis, can confirm or exclude Down syndrome. Ultrasound alone cannot. Tietz Textbook of Laboratory Medicine, Down Syndrome section.

The SMFM guidance on isolated soft markers specifically advises that for an isolated thickened nuchal fold after a negative cell-free DNA result, no further chromosome evaluation is required; with negative serum screening or no prior screening, NIPT and/or amniocentesis can be discussed.

Ask your doctor for:

the actual nuchal-fold measurement in mm
whether it was truly isolated
results of any prior first-trimester, quad-screen, or NIPT testing
referral to maternal-fetal medicine/genetic counseling if not already arranged.

Maternal herpes zoster infection in pregnancy

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herpes zoster shingles pregnancy fetal risk treatment acyclovir guideline

Maternal herpes zoster (shingles) in pregnancy is usually reassuring for the fetus. It is reactivation of prior varicella-zoster virus infection, so the mother already has VZV antibodies. Unlike primary varicella (chickenpox), shingles is not generally associated with congenital varicella syndrome or an increased risk of fetal loss.

What to do

Contact your obstetrician or maternity unit promptly, ideally within 72 hours of rash onset, because antiviral treatment may reduce severity and duration of the rash and pain.
Diagnosis is often clinical: a painful, one-sided, blistering rash in a dermatome. If uncertain, a swab from a fresh blister for VZV PCR can confirm it.
Oral acyclovir or valacyclovir may be prescribed by your clinician. Available human data have not shown a major birth-defect signal with acyclovir/valacyclovir exposure.
Use pregnancy-appropriate pain relief, usually acetaminophen/paracetamol unless your clinician advises otherwise.

When urgent assessment is needed

Seek same-day urgent care or emergency assessment if:

rash involves the eye, forehead, tip of nose, or ear
rash is widespread, you have shortness of breath, severe headache, confusion, or high fever
you are immunocompromised
pain or symptoms are severe.

Transmission precautions

Shingles can transmit VZV by direct contact with fluid from uncrusted blisters, causing chickenpox in a person who is not immune. Keep the rash covered, do not touch/scratch it, and wash hands. Avoid direct contact with people who are non-immune and at high risk, including pregnant people without prior chickenpox/vaccination, newborns, and severely immunocompromised people, until all lesions have crusted.

This is different from a first episode of chickenpox in pregnancy, which has substantially different maternal and fetal implications. Maternal-fetal medicine text notes that herpes zoster occurs in someone who already has VZV antibody, whereas primary varicella is the major pregnancy concern. The RCOG chickenpox guidance covers the higher-risk primary-varicella scenario.

How is shingles different from primary chickenpox in pregnancy?

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RCOG varicella chickenpox pregnancy fetal varicella syndrome shingles risk pregnancy

Both are caused by varicella-zoster virus (VZV), but they represent different infections and have very different pregnancy implications.

Feature	Primary chickenpox (varicella)	Shingles (herpes zoster)
What it is	First VZV infection in someone without immunity	Reactivation of VZV already dormant after prior chickenpox or vaccination
Typical rash	Widespread, itchy crops of spots and blisters, often with fever and malaise	Painful/tingling, usually one-sided band of grouped blisters in one dermatome
Maternal immunity	No established VZV immunity initially	Existing VZV antibodies are present
Maternal risk	Adults, including pregnant people, can become seriously ill, especially with varicella pneumonia	Usually localized illness; main issue is pain and, rarely, eye or disseminated disease
Fetal risk	Can cause fetal varicella syndrome if acquired in the first 20 to 28 weeks, and can create neonatal risk if illness occurs around delivery	Usually no meaningful fetal risk in an immunocompetent mother
Pregnancy follow-up	Obstetric and fetal-medicine review is usually needed	Usually routine obstetric care, unless severe, disseminated, uncertain diagnosis, or eye involvement
Infectiousness	Highly contagious by respiratory spread and direct contact until lesions crust	Mainly spread by direct contact with blister fluid. It can give a non-immune contact chickenpox, not shingles

Why chickenpox is more concerning

With primary chickenpox, the virus can enter the bloodstream and cross the placenta. If it occurs in the first half of pregnancy, there is a small risk of fetal varicella syndrome, which can include skin scarring, limb hypoplasia, eye abnormalities, and brain injury. The risk is small, around 1% to 2% overall in affected pregnancies before 20 weeks, but it warrants specialist assessment. Dermatology 5e, p. 1713.

Chickenpox occurring from 5 days before to 2 days after delivery is especially important because the newborn may develop severe neonatal varicella before receiving protective maternal antibodies.

Why shingles is usually reassuring

Shingles means the virus has reactivated locally in nerve tissue in a person with pre-existing immunity. Maternal antibodies and the usual absence of significant bloodstream spread make fetal infection very unlikely. The RCOG patient guidance states that shingles during pregnancy is usually mild and carries no risk to the mother or baby.

Practical action

Chickenpox rash or exposure without known immunity: contact the maternity unit or obstetrician urgently, ideally the same day.
Shingles: contact the obstetric clinician promptly, especially if within 72 hours of rash onset, to discuss antiviral treatment. Seek urgent care for eye/face involvement, a widespread rash, breathing symptoms, or immunosuppression.
Keep either rash covered where possible and avoid contact with non-immune pregnant people, newborns, and immunocompromised people until lesions are fully crusted.

The RCOG clinical guideline recommends fetal-medicine referral and detailed ultrasound assessment after maternal primary chickenpox in pregnancy, which is not routinely required for uncomplicated maternal shingles.

Fetal macrocephaly

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ISUOG fetal macrocephaly prenatal ultrasound evaluation head circumference 97th percentile guideline

Fetal macrocephaly means the fetal head circumference is larger than expected for gestational age, usually above the 98th percentile or more than 2 standard deviations above the mean. It is an ultrasound finding, not a diagnosis. ISUOG patient guidance

Common explanations

Normal familial large head: often isolated, especially if one or both parents have a large head circumference.
Incorrect gestational dating or measurement variation.
Large overall fetus: head, abdomen, and limbs are all proportionally large.
Extra fluid in the brain ventricles: ventriculomegaly or hydrocephalus.
Less commonly, a brain-development difference, skeletal dysplasia, or genetic/chromosomal syndrome, particularly if there are other anomalies or disproportionate growth.

What should be assessed

A maternal-fetal medicine specialist should review:

The exact head circumference, BPD, percentile, and Z-score, and whether measurements are increasing rapidly on serial scans.
Whether the head is large in proportion to the abdomen and femur length.
Detailed fetal neurosonography, including ventricles, midline structures, cerebellum, posterior fossa, and brain shape.
A careful search for non-brain structural findings.
Parental head circumferences and family history.

If the finding is confirmed, follow-up ultrasound is commonly used to monitor growth and ventricular size. Fetal MRI can add detail when ultrasound cannot fully assess the brain, and amniocentesis with chromosomal microarray or more extensive genetic testing may be offered when there are associated anomalies, marked/progressive macrocephaly, or concern for a genetic condition. ISUOG evaluation advice

Prognosis

If macrocephaly is isolated, brain anatomy is normal, and it is stable on repeat scans, the outcome is often good and may represent a familial normal variant. Prognosis depends much more on the cause and any associated brain or body abnormalities than on head size alone.

Large head size can affect delivery planning near term. The obstetric team will reassess fetal head size, presentation, and the likelihood of cephalopelvic disproportion; cesarean delivery is sometimes considered when macrocephaly is substantial. Creasy & Resnik’s Maternal-Fetal Medicine, Antenatal Management section.

Useful details to obtain from the report are: gestational age, HC percentile or Z-score, BPD, ventricular measurement in mm, whether the scan says “isolated,” and any other noted abnormalities.

Preaxial polydactyl

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What conditions are associated with fetal preaxial polydactyly?

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