Rare autosomal trisomies are not rare and often associated with poor obstetric outcomes. They should be discussed with the clinician to guide management. Pregnancy outcomes varied by chromosome being generally favourable for some (eg, trisomy 7) and poor for others (eg, trisomy 22). In the presence of a RAT, pregnancy-associated plasma protein-A is predictive of placental dysfunction and fetal growth restriction.

Prenatal diagnosis of sex discordance is a relatively new phenomenon. Prior to cell-free DNA testing, the diagnosis of a disorder of sexual differentiation was serendipitous, either through identification of ambiguous genitalia at the midtrimester morphology ultrasound or discovery of genotype-phenotype discordance in cases where preimplantation genetic diagnosis or invasive prenatal testing had occurred.

A ccording to the Rotterdam consensus, 1 polycystic ovarian syndrome (PCOS) is defined by the presence of two of three of the following criteria: oligo-anovulation, hyperandrogenism and polycystic ovaries (≥ 12 follicles measuring 2-9 mm in diameter and/or an ovarian volume > 10 mL in at least one ovary). The sonographic criteria were based on a study published in 2003 by Jonard et al., 2 where patients with PCOS were found to have significantly more follicles in the 2-5 mm range than a control group comprised of women with tubal or male factor infertility. The decision to set the cut-off at 12 follicles measuring between 2 and 9 mm resulted from a compromise between specificity (99%) and sensitivity (75%), noting that narrowing the range to between 2 and 5 mm did not improve the diagnostic power. A suggestion was made to repeat the assessment in a subsequent cycle if the ovary was enlarged and its antral follicle count obscured by a dominant follicle (>10 mm) or a corpus luteum. 3 There is no consensus on how to classify ovaries with a high follicle count when using oral contraception or other exogenous hormones or when there is evidence of a dominant follicle or corpus luteum in successive cycles. Is the Rotterdam consensus still appropriate?Over the 15 years since the Rotterdam consensus, increasing use of transvaginal assessment and technological improvements in ultrasound resolution have resulted in 20%-30% of regularly cycling, normo-ovulatory women satisfying the Rotterdam criteria for polycystic ovarian morphology 4 and even more in a younger demographic. 5 The sonographic assessment has, over time, become the dominant indicator of PCOS and is often either overinterpreted or misinterpreted as a de facto diagnostic test, often ignoring the presence of a dominant follicle or corpus luteum. These women may then be inappropriately considered 'polycystic' without having the requisite clinical or biochemical correlates.Post-menarcheal teenagers almost always have at least one ovary with > 12 visible follicles and labelling them as 'polycystic' can lead to unnecessary investigations, inappropriate management and stigmatisation. The same is true for women with regular, ovulatory cycles attending ultrasound for reasons other than fertility assessment, who happen to have 15 visible antral follicles and a dominant follicle or corpus luteum. Being wrongfully labelled 'polycystic' may also adversely affect selfesteem and influence women's choices around their diet and use of contraception.

(Abstracted from Prenatal Diagn 2018;38(10):765–771) Noninvasive prenatal testing (NIPT) analyzes cell-free DNA (cfDNA) in maternal plasma, which is a combination of DNA from maternal cells and from placental cytotrophoblast. The technique of massively parallel sequencing (MPS) sequences and counts large numbers of unique, single-locus DNA fragments and assigns them to the chromosome of origin.