What specific care is recommended at 16 weeks of gestation?

Specific Care Recommended at 16 Weeks of Gestation

At 16 weeks gestation, the primary specific intervention is initiating ultrasound surveillance for twin-twin transfusion syndrome (TTTS) in all monochorionic-diamniotic (MCDA) twin pregnancies, with scans performed at least every 2 weeks until delivery. 1

For Monochorionic-Diamniotic Twin Pregnancies

Mandatory Surveillance Initiation

• Begin ultrasound surveillance for TTTS at exactly 16 weeks gestation for all MCDA twin pregnancies (GRADE 1C recommendation). 1
• Continue this surveillance at minimum every 2 weeks throughout pregnancy until delivery, with more frequent monitoring if clinical concerns arise. 1

Required Ultrasound Components

The surveillance ultrasound must include: 1

• Assessment of amniotic fluid volumes on both sides of the intertwin membrane
• Evaluation for presence or absence of urine-filled fetal bladders in both twins
• Doppler study of the umbilical arteries (ideally incorporated)

Additional Doppler Surveillance Consideration

• Consider incorporating middle cerebral artery (MCA) Doppler peak systolic velocity (PSV) determinations into all monochorionic twin ultrasound surveillance beginning at 16 weeks (GRADE 1C recommendation). 1
• This helps screen for twin anemia-polycythemia sequence (TAPS), though universal screening remains somewhat controversial due to lack of consensus on optimal management strategies. 1

For Singleton Pregnancies

Routine Anatomic Survey Timing

• While the standard detailed anatomic ultrasound is typically performed at 18-22 weeks, some centers may begin earlier screening around 16 weeks in specific circumstances. 2
• Second trimester ultrasound (14-24 weeks) improves detection of major fetal abnormalities and allows for earlier diagnosis and counseling. 2

Special Populations at 16 Weeks

For fetuses with increased nuchal translucency (≥3.5 mm) detected in first trimester but normal chromosomal microarray: 3

• A detailed 16-week ultrasound can detect approximately 26.5% of structural defects that would otherwise be identified at the traditional 20-24 week scan
• This earlier detection allows for earlier counseling and management decisions

Critical Clinical Pitfalls

Monochorionic Twin Surveillance

• Failure to establish chorionicity in the first trimester is a major pitfall - chorionicity determination should occur before 16 weeks to ensure appropriate surveillance protocols are in place. 1
• Missing the 16-week surveillance initiation window delays detection of TTTS, which can present as early as 16 weeks and requires intervention between 16-26 weeks for optimal outcomes. 1

Surveillance Frequency Errors

• Do not perform surveillance less frequently than every 2 weeks for MCDA twins, as TTTS can develop rapidly. 1
• Increase surveillance frequency beyond every 2 weeks if any clinical concerns arise. 1

Incomplete Ultrasound Assessment

• Do not omit assessment of fetal bladders - absence of a visible bladder in the donor twin is a key diagnostic criterion for TTTS. 1
• Do not skip Doppler studies - umbilical artery Doppler abnormalities provide critical prognostic information. 1

Referral Considerations

• Any MCDA twin pregnancy diagnosed with TTTS at 16 weeks or later should be referred to a fetal intervention center for evaluation and potential fetoscopic laser surgery, particularly for stage II-IV disease. 1
• Fetoscopic laser surgery is the standard treatment for stage II-IV TTTS presenting between 16-26 weeks gestation (GRADE 1A recommendation). 1