P09.10: Prenatal diagnosis of achondroplasia in the second trimester of pregnancy using the biparietal diameter/femur length ratio

Abstract

We present a case of a 22 year-old nulliparous woman who presented for a routine early pregnancy ultrasound scan for reassurance which demonstrated a viable pregnancy with a Crown-rump length of 29mm (9 weeks and 5 days gestation). On two-dimensional transvaginal imaging, the fetal heart beat was present. A three-dimensional volume of the fetus was acquired and examined using Crystal Vue and Realistic Vue™ rendering software, enabling visualisation of the fetal limbs, fingers and spine.Limb, and particularly hand malformations, may be sporadic and isolated but are often associated with syndromes or chromosomal aneuploidy. Earlier detection of these anomalies will allow more thorough anatomical assessment and a discussion regarding further pre-natal testing, if appropriate, to occur well before the early second trimester. While traditional imaging methods enable detection of large neural tube defects in the first trimester, Crystal Vue and Realistic Vue™ rendering may allow subtler skeletal abnormalities to be detected. Novel rendering software has the potential to enable more detailed assessment of the fetal skeletal system to occur in the first trimester of pregnancy.Supporting information can be found in the online version of this abstract Unilateral tibial hemimelia is an anomaly characterised by the absence of the tibia. Tibial hemimelia is a very rare disease with an incidence of 1 in 1,000,000 live births. It is characterised by deficiency of tibia with relatively intact fibula. It causes marked shortening of the involved extremity with a severe equinovarus deformity. It may be isolated or associated with other anomalies. We report a case showing the absence of tibia in a 25-year-old primigravida diagnosed at 13 weeks of gestation who was referred to our centre for a routine first trimester scan. She had no notable history of intake of any medication or maternal infection. Ultrasound examination showed a single viable fetus of 13 weeks gestation which revealed foreshortening of the right lower limb with associated flexion at the knee and with talipes equino varus deformity of the right foot. Careful examination of right lower leg showed the absence of the tibia and the flexion at the knee. This was due to the atrophy of the quadriceps muscle. The left leg and the upper limbs were unremarkable. The aneuploidy markers on ultrasound were also normal. In view of the future disability of the baby, the couple opted for the termination of pregnancy. The abortus showed the same findings as seen on ultrasound and the autopsy also confirmed the diagnosis of unilateral tibial hemimelia. Results: Of the 33 cases, 20 cases were diagnosed as thanatophoric dysplasia (TD) and 13 cases were diagnosed as achondroplasia (ACH). By prenatal ultrasonographic examination, positive predictive values were 83% and 65% for diagnosis of TD and ACH respectively. Nine cases of TD and all 13 cases of ACH were confirmed by FGFR3 gene and the remaining 11 cases of TD were diagnosed by postmortem autopsies. In the cases of TD, shortening o...