What's new in guidance? Updates in obstetrics

In February 2025, the RCOG published a partial update to the existing Green-top Guideline (GTG) on the Management of monochorionic twin pregnancy,1 previously published in 2016.2 The guideline was updated to include the following modified or new recommendations. The guideline now recommends that fetal sex determination can provide additional information to guide the determination of chorionicity when this is assessed after 14 weeks of pregnancy. The new guideline acknowledges digitisation of maternity records and therefore recommends that evidence of chorionicity (image of membrane insertion into the placenta) can now be documented electronically, rather than with a printed thermal image. Following the publication of the updated NICE guideline ‘Twin and Triplet Pregnancy’,3 the new RCOG GTG also recommends that cell-free fetal DNA testing (also known as non-invasive prenatal testing, NIPT) can be offered in monochorionic twin pregnancies, contingent on the results of the first-trimester combined test for trisomies 13, 18 and 21, as for singleton pregnancies. With regard to screening for and management of specific complications of monochorionic twin pregnancies, and twin-to-twin transfusion syndrome (TTTS) in particular, RCOG now recommends an increase to weekly scanning if there are concerns about differences in amniotic fluid levels between the two amniotic sacs in the second or third trimester. Regarding the management of TTTS, RCOG now advocates for fetoscopic laser ablation using the SOLOMON technique (serial sequential ablation, followed by equatorial laser dichorionisation). All other recommendations remain unchanged. This new RCOG Green-top Guideline was published in April 2025.4 The guideline acknowledges variation internationally in screening for and management of thyroid disorders, influenced by differences in population iodine deficiency. It also acknowledges controversies in testing and management of thyroid disorders during the peri-conception and peri-natal periods. Whilst the guideline is evidenced where possible, some practice points have been developed following consensus of a wide range of specialist opinions. In the introductory section, the authors provide a useful table summarising interpretation of thyroid functions tests (TFTs) and implicated diagnoses. The guideline recommends that trimester and manufacturer specific reference ranges for TFTs are applied during pregnancy; where these are not provided by the local laboratory, suggested references are contained within the appendices. A dietary or supplemental increase in iodine is recommended when planning and during pregnancy and during breastfeeding. Titration of levothyroxine pre-pregnancy in women with overt hypothyroidism, or severe subclinical hypothyroidism (thyroid-stimulating hormone, TSH >10 mU/L), is recommended to achieve a pre-conception TSH level ≤ 2.5 mU/L. Women should then be counselled to double their dose of levothyroxine on 2 days per week, from the date of a positive pregnancy test. For women on levothyroxine, TFTs should then be offered 4–6 weekly prior to 20 weeks of pregnancy, and then again at 28 weeks of gestation. Levothyroxine should be titrated to keep the TSH ≤ 2.5 mU/L, while maintaining T4 within the local trimester-specific reference range. Pre-conception/antenatal levothyroxine can also be considered for women with lesser severity of subclinical hypothyroidism (TSH above the upper non-pregnant threshold, but below 10), especially if the woman is known to be thyroid peroxidase (TPO) antibody positive or the hypothyroidism is diagnosed in the first trimester, aiming to keep the TSH ≤ 2.5 mU/L. Levothyroxine is not recommended for euthyroid women who are known to be TPO antibody positive, nor is routine testing for this antibody in euthyroid women. However, if a woman is already known to be TPO antibody positive, she can be offered TFTs in the first trimester, and repeated at 20 weeks of gestation. Regarding care for women with hyperthyroidism in the pre-conception and prenatal periods, the RCOG recommends that women who require medical treatment are preferably prescribed propylthiouracil (PTU) rather than carbimazole (CMZ) at the lowest effective dose to maintain free T4 concentrations in the upper half of the reference range. If the woman conceives while taking CMZ, she should ideally be switched to PTU as soon as possible, and before 10 weeks of pregnancy. This is because of its potentially teratogenic effects (associations with dysmorphic features, aplasia cutis, choanal and oesophageal atresia, abdominal wall defects, urinary and eye abnormalities, and ventricular septal defects). If a woman on a low dose of treatment for hyperthyroidism conceives after 6 months of being euthyroid, clinicians should consider discontinuing the medication, with close thyroid monitoring. During the first half of pregnancy, women on anti-thyroid medications should be offered TFTs every 2–4 weeks; after 20 weeks of gestation, the testing interval can be reduced to 4–8 weeks. Following a new finding of suppressed TSH, accompanied by a high free T4 level, gestational transient thyrotoxicosis can be distinguished from Graves' disease using a range of clinical features, measurement of TSH-receptor antibodies (TRAb), and free-T3. Gestational transient thyrotoxicosis requires supportive management only.