If you are expecting more than one baby (twins, triplets or more), the options for prenatal screening for chromosome differences are different from singleton pregnancies.

If you are having twins

If you are pregnant with twins, the options for prenatal screening include:

• Nuchal translucency (NT) ultrasound
  • as part of enhanced first trimester screening (eFTS)
• Non-invasive prenatal testing (NIPT)

Maternal serum screening (MSS) is not available in twin pregnancies.

If you are pregnant with more than two babies

If you are having triplets, quadruplets, or more, your option for screening the pregnancy for chromosome differences is limited to:

• Nuchal translucency (NT) ultrasound only

The NT measurement will be combined with maternal (or egg donor) age to calculate a fetus-specific risk for Down syndrome and/or trisomy 18.

Vanishing twin

A vanishing twin scenario occurs when a twin or fetus in a multiple pregnancy disappears during the pregnancy as the result of a miscarriage of one fetus. This fetal tissue is then absorbed by the other fetus, the placenta or the mother.

In the case of a vanishing twin, the recommended option for prenatal screening is:

• if there is access to NT ultrasound - nuchal translucency (NT) ultrasound with MSS bloodwork
• if there is no access to NT ultrasound – MSS bloodwork alone

If MSS blood work is drawn, it is recommended that it be drawn at least 8 weeks after the estimated time of miscarriage of the fetus.