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ISUOG Practice Guidelines (updated): role of ultrasound in twin pregnancy

ISUOG · 2025 · international

Source and licence

Authors
A. Khalil, A. Sotiriadis, A. Baschat et al.
Title
ISUOG Practice Guidelines (updated): role of ultrasound in twin pregnancy
Journal
Ultrasound in Obstetrics & Gynecology, 2025
DOI
10.1002/uog.29166
Licence
CC BY 4.0
Changes
Verbatim excerpts; formatting adapted

Full text retrieved 2026-10-27 from Europe PMC · PMC11788470

Licence statement of the original publication

This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

This page reproduces excerpts of the original publication; the original is authoritative. It has not been reviewed by a physician, does not state a recommendation of Medelix and does not replace medical advice. The guideline may have been updated since.

Open the original publication →Full text on Europe PMC

Recommendations

Verbatim, with grade of recommendation or strength of consensus where given.

Dating of twin pregnancy

  • Twin pregnancies conceived spontaneously should ideally be dated prior to 13 + 6 weeks of gestationGRADE OF RECOMMENDATION: D
  • In twin pregnancies conceived spontaneously, the larger of the two crown–rump lengths (CRLs) should be used to estimate gestational ageGRADE OF RECOMMENDATION: C
  • Fetal head circumference of the larger twin should be used to date the pregnancy at or beyond 14 weeks' gestationGRADE OF RECOMMENDATION: D
  • Twin pregnancies conceived via in‐vitro fertilization should be dated using the age of the embryo and the date of transferGRADE OF RECOMMENDATION: C

Determining chorionicity and amnionicity in twin pregnancy

  • Chorionicity should be determined prior to 13 + 6 weeks of gestation based on as many ultrasound characteristics as possible, including the entire intertwin septum (at the site of insertion of the amniotic membrane into the placenta, using the lambda sign or the T sign), membrane thickness and number of placental massesGRADE OF RECOMMENDATION: D
  • An ultrasound image demonstrating the chorionicity should be kept in the medical records for future reference (GOOD PRACTICE POINT).
  • If it is not possible to determine chorionicity by transabdominal or transvaginal ultrasound in the routine setting, a second opinion should be sought from a tertiary referral center (GOOD PRACTICE POINT).
  • In monochorionic twin pregnancies, amnionicity can be determined from 8 weeks onwards, when the amniotic sac becomes visible on ultrasound scan. MCMA twin pregnancies should be referred to a tertiary center with expertise in their management (GOOD PRACTICE POINT).

Labeling of twin fetuses

  • The labeling of twin fetuses should follow a reliable and consistent strategy and should be documented clearly in the woman's notes (GOOD PRACTICE POINT).
  • The labeling of twin fetuses should be based on the lateral or vertical orientation of the gestational sacs and include as many parameters as possible (GOOD PRACTICE POINT).

Routine monitoring of twin pregnancy with ultrasound

  • Women with an uncomplicated dichorionic twin pregnancy should have a first‐trimester scan, a second‐trimester anomaly scan and scans every 4 weeks thereafter. Complicated dichorionic twins should be scanned more frequently, depending on the condition and its severity (GOOD PRACTICE POINT).
  • Uncomplicated monochorionic twins should have a first‐trimester scan and be scanned every 2 weeks after 16 weeks, in order to detect TTTS in a timely manner. Complicated monochorionic twins should be scanned more frequently, depending on the condition and its severityGRADE OF RECOMMENDATION: C

Screening for chromosomal abnormalities in twin pregnancy

  • Screening for trisomy 21 in twin pregnancy should be offered in the first trimester. The most accurate test that can be offered from 10 weeks' gestation uses cell‐free DNA (cfDNA) in the maternal blood. The detection rate (DR) of non‐invasive prenatal testing (NIPT) for trisomy 21 using cfDNA may be slightly lower in twins than in singletons, but it is the most accurate method of screening for trisomy 21 in twin pregnancy. Data on the screening performance using NIPT for other trisomies (trisomies 18 and 13) are limited and further research is neededGRADE OF RECOMMENDATION: B
  • If NIPT is not available, screening for trisomy 21 should be performed in the first trimester using the combined test (nuchal translucency thickness (NT), free beta‐human chorionic gonadotropin (β‐hCG) level and pregnancy‐associated plasma protein‐A (PAPP‐A) level). An alternative is a combination of maternal age and NT, depending on the clinical context and/or health settingGRADE OF RECOMMENDATION: B
  • In case of a vanished twin, just NT in combination with maternal age should be used for risk estimation. An alternative could be NT in combination with maternal age and free β‐hCG levelGRADE OF RECOMMENDATION: B

Invasive prenatal diagnosis in twin pregnancy

  • CVS should be preferred to amniocentesis in dichorionic twin pregnancy, as it provides an earlier prenatal diagnosisGRADE OF RECOMMENDATION: D
  • In MCDA twin pregnancy complicated by discordant anomaly, the option of dual amniocentesis should be consideredGRADE OF RECOMMENDATION: D

Implications of discordance in NT or CRL in the first trimester in twin pregnancy

  • The management of twin pregnancy with CRL discordance ≥ 10% or NT discordance ≥ 20% should be discussed with a fetal medicine expert in accordance with local guidelines and resource availability (GOOD PRACTICE POINT).

Ultrasound screening for structural abnormalities in twin pregnancy

  • Twin fetuses should be assessed for the presence of any major anomalies at the first‐trimester scan, and a routine second‐trimester (anomaly) scan should be performed at around 20 (18–22) weeks' gestation (GOOD PRACTICE POINT).
  • Fetal cardiac assessment should be performed in monochorionic twins. The operator performing this assessment will depend on the resources and healthcare setting (GOOD PRACTICE POINT).

Managing twin pregnancy discordant for fetal anomaly

  • Twin pregnancies discordant for fetal anomaly should be referred to a regional fetal medicine center (GOOD PRACTICE POINT).

Selective feticide in twin pregnancy

  • In dichorionic twin pregnancy, selective feticide is performed by ultrasound‐guided intracardiac or intrafunicular injection of potassium chloride or lignocaine, preferably in the first trimesterGRADE OF RECOMMENDATION: B
  • When the diagnosis is made in the second trimester, the woman might opt for late selective termination in the third trimester, if the law permits (GOOD PRACTICE POINT).
  • Selective feticide in monochorionic twin pregnancy is performed by cord occlusion, intrafetal laser ablation, microwave ablation or radiofrequency ablation (RFA)GRADE OF RECOMMENDATION: B

Screening for risk of preterm birth in twin pregnancy

  • Cervical‐length measurement (ideally transvaginally) is the preferred method of screening for preterm birth in twins; 25 mm is a pragmatic cut‐off between 18 and 24 gestational weeksGRADE OF RECOMMENDATION: B
  • Cervical length should be measured at the anatomy scan and, in case of additional risk factors, once again before 24 weeksGRADE OF RECOMMENDATION: C
  • Prophylactic use of progesterone is not recommended for the prevention of preterm birth in unselected twin pregnancyGRADE OF RECOMMENDATION: A
  • Prophylactic use of vaginal progesterone may be considered in twin pregnancy with cervical length ≤ 25 mmGRADE OF RECOMMENDATION: C
  • A combined strategy of physical‐exam‐indicated cerclage, antibiotics and tocolytics may be considered in asymptomatic twin pregnancy with dilated cervix before 24 weeks of gestationGRADE OF RECOMMENDATION: C
  • Cervical cerclage may be considered when cervical length is ≤ 15 mm before 24 weeks of gestationGRADE OF RECOMMENDATION: C

Diagnostic criteria and investigations for sFGR

  • A discordance cut‐off of 20% seems acceptable to distinguish pregnancies at increased risk of adverse outcomeGRADE OF RECOMMENDATION: B

Screening for FGR in twin pregnancy

  • A combination of head, abdomen and femur measurements performs best in calculating EFWGRADE OF RECOMMENDATION: B
  • If intertwin discordance is ≥ 25% or the EFW of one twin is < 10th centile, a referral should be made to a specialist fetal medicine center (GOOD PRACTICE POINT).

Classification of monochorionic twin pregnancy complicated by sFGR

  • Classification of sFGR in monochorionic twins has traditionally relied on the pattern of end‐diastolic velocity on UA Doppler (GOOD PRACTICE POINT).

Managing dichorionic twin pregnancy complicated by sFGR

  • In dichorionic twin pregnancies, sFGR should be monitored similarly to growth‐restricted singletons (GOOD PRACTICE POINT).

Managing monochorionic twin pregnancy complicated by sFGR

  • In monochorionic twin pregnancy complicated by sFGR, fetal Doppler should be assessed at least weekly (GOOD PRACTICE POINT).
  • If there is a substantial risk of fetal demise of one cotwin before 26 weeks, selective termination may be consideredGRADE OF RECOMMENDATION: D

Managing the surviving twin after demise of its cotwin

  • When single IUD occurs in a twin pregnancy, the woman should be referred to a tertiary‐level center with relevant expertise (GOOD PRACTICE POINT).

Contents of the original publication

The section headings of the original.

  • Clinical Standards Committee
  • INTRODUCTION
  • OUTLINE/SCOPE
  • IDENTIFICATION AND ASSESSMENT OF EVIDENCE
  • RECOMMENDATIONS
  • Dating of twin pregnancy
  • Determining chorionicity and amnionicity in twin pregnancy
  • Labeling of twin fetuses
  • Routine monitoring of twin pregnancy with ultrasound
  • Screening for chromosomal abnormalities in twin pregnancy
  • Invasive prenatal diagnosis in twin pregnancy
  • Implications of discordance in NT or CRL in the first trimester in twin pregnancy
  • Ultrasound screening for structural abnormalities in twin pregnancy
  • Managing twin pregnancy discordant for fetal anomaly
  • Selective feticide in twin pregnancy
  • Screening for risk of preterm birth in twin pregnancy
  • Screening, diagnosis and management of FGR in twin pregnancy
  • Managing the surviving twin after demise of its cotwin
  • COMPLICATIONS UNIQUE TO MONOCHORIONIC TWIN PREGNANCY
  • Screening, diagnosis, staging and management of TTTS
  • Screening, diagnosis and management of TAPS
  • Management of TRAP sequence
  • Management of MCMA twins
  • Diagnosis and management of conjoined twins
  • GUIDELINE AUTHORS
  • CITATION

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