Quality statement 1: Determining chorionicity and amnionicity

Quality standard

Quality statement
Rationale
Quality measures
What the quality statement means for different audiences
Source guidance
Definitions of terms used in this quality statement
Equality and diversity considerations

Quality statement 1: Determining chorionicity and amnionicity

Quality statement

Women with a multiple pregnancy have the chorionicity and amnionicity of their pregnancy determined using ultrasound and recorded between 11⁺² weeks and 14⁺¹ weeks.

Rationale

If fetuses share a placenta, there is a greater risk of complications. Determining chorionicity and amnionicity allows women to be assigned the correct plan of care for their pregnancy.

Pregnancy risks, clinical management and subsequent outcomes are different for monochorionic and dichorionic twin pregnancies (and for monochorionic, dichorionic and trichorionic triplet pregnancies). Therefore, accurate determination of chorionicity is important.

Quality measures

The following measures can be used to assess the quality of care or service provision specified in the statement. They are examples of how the statement can be measured, and can be adapted and used flexibly.

Structure

Evidence of local arrangements to ensure that women with a multiple pregnancy have an ultrasound scan between 11⁺² weeks and 14⁺¹ weeks to determine and record the chorionicity and amnionicity of their pregnancy.

Data source: Local data collection.

Process

The proportion of women with a multiple pregnancy who receive an ultrasound scan between 11⁺² weeks and 14⁺¹ weeks to determine and record the chorionicity and amnionicity of their pregnancy.

Numerator – the number of women in the denominator who received an ultrasound scan between 11⁺² weeks and 14⁺¹ weeks to determine and record the chorionicity and amnionicity of their pregnancy.

Denominator – the number of women with a multiple pregnancy of greater than 14⁺¹ weeks' gestation.

Data source: Local data collection. The NHS Digital Maternity Services Data Set collects data on:

Offer status – dating ultrasound scan (global number 17201960).
Gestation – dating ultrasound scan (global number 17202010).
Number of fetuses – dating ultrasound scan (global number 17202020).

Outcome

Determination of chorionicity and amnionicity.

Data source: Local data collection.

What the quality statement means for different audiences

Service providers ensure that systems are in place for women with a multiple pregnancy to have an ultrasound scan between 11⁺² weeks and 14⁺¹ weeks to determine and record the chorionicity and amnionicity of their pregnancy.

Healthcare practitioners ensure that women with a multiple pregnancy have an ultrasound scan between 11⁺² weeks and 14⁺¹ weeks to determine and record the chorionicity and amnionicity of their pregnancy.

Commissioners ensure that they commission specialist services that provide ultrasound scanning between 11⁺² weeks and 14⁺¹ weeks for women with a multiple pregnancy to determine and record the chorionicity and amnionicity of their pregnancy.

Women who are pregnant with twins or triplets (referred to as a multiple pregnancy) have an ultrasound scan between 11 weeks 2 days and 14 weeks 1 day of their pregnancy. This is to see whether the babies share the same placenta (chorionicity) and amniotic sac (amnionicity). This information is recorded in the woman's notes.

Source guidance

Twin and triplet pregnancy. NICE guideline NG137 (2019, updated 2024), recommendations 1.1.1, 1.1.3, and 1.3.7 to 1.3.10

The timing of the ultrasound scan is also shown in the Twins Trust multiple pregnancy antenatal care proforma and care pathways.

Definitions of terms used in this quality statement

Multiple pregnancy

A multiple pregnancy is defined as a twin or triplet pregnancy. [Expert opinion]

Chorionicity

The number of chorionic (outer) membranes that surround babies in a multiple pregnancy. If there is only 1 membrane, the pregnancy is described as monochorionic; if there are 2, the pregnancy is described as dichorionic; and if there are 3, the pregnancy is trichorionic. Monochorionic twin pregnancies and monochorionic/dichorionic triplet pregnancies carry higher risks because babies share a placenta. [NICE's guideline on twin and triplet pregnancy, terms used in this guideline]

Amnionicity

The number of amnions (inner membranes) that surround babies in a multiple pregnancy. Pregnancies with 1 amnion (so that all babies share an amniotic sac) are described as monoamniotic; pregnancies with 2 amnions are diamniotic; and pregnancies with 3 amnions are triamniotic. [NICE's guideline on twin and triplet pregnancy, terms used in this guideline]

Ultrasound scan

An ultrasound scan is used to determine chorionicity based on the number of placental masses, the Lambda or T‑sign and the presence of amniotic membrane(s) and membrane thickness. [NICE's guideline on twin and triplet pregnancy, recommendation 1.1.3]

Note: NICE's guideline on antenatal care recommends determination of gestational age from 10 weeks 0 days. However, the aim in NICE's guideline on twin and triplet pregnancy is to minimise the number of scan appointments that women need to attend within a short time, especially if it is already known that a woman has a twin or triplet pregnancy (for example, as a result of IVF treatment).

Recording the chorionicity and amnionicity

The chorionicity and amnionicity of the pregnancy should be documented in the ultrasound report. An electronic copy of the ultrasound report and an ultrasound image (of Lambda or T sign) should be stored on the radiology reporting and picture archiving system. Hard copies of the report should be printed out and placed in the woman's hand-held maternity notes and their hospital notes. [Expert opinion]

Equality and diversity considerations

Some pregnant women have complex social needs and may be less likely to access or maintain contact with antenatal care services. Examples of women with complex social needs include, but are not limited to, women who:

have a history of substance misuse (alcohol or drugs)
have recently arrived in the UK as a migrant, asylum seeker or refugee
have difficulty speaking or understanding English
are aged under 20 years
have experienced domestic abuse
are living in poverty
are homeless.

It is therefore appropriate that professionals give special consideration to women with complex social needs. NICE's guideline on pregnancy and complex social factors includes recommendations on how to make antenatal care accessible to pregnant women with complex social needs and how to encourage women to maintain ongoing contact with maternity services.