What to Expect When You’re Expecting….a Baby with Tetrasomy 18

Benjamin Dossetter, MS32, Jessica Bennett, MD, MPH1, 1Tufts University School of Medicine and Floating Hospital for Children at Tufts Medical Center, Boston, MA; 2Tufts University School of Medicine, Somerville

Meeting: Hospital Medicine 2018; April 8-11; Orlando, Fla.

Abstract number: 392

Categories: Clinical Vignettes, Hospital Medicine 2018, Pediatric

Keywords: , , , ,

Case Presentation: This is the case of a 39-year old, G3P1001 woman with fetal aneuploidy identified on prenatal screening. Her pregnancy was conceived via anonymous sperm donor, whom had been used for two previous healthy and uncomplicated pregnancies. The mother underwent non-invasive prenatal testing (NIPT) at 10 weeks gestation, which was reported as positive for trisomy 18. Follow-up chorionic villous sampling yielded an abnormal direct FISH result for aneuploidy of the 18th chromosome, however the cultured specimen revealed a fetal karyotype of 46XX. At 17 weeks gestation, amniocentesis confirmed the final fetal karyotype result of 47XX, i18p (4) – 46XX (22), consistent with mosaicism for tetrasomy of 18p. Ultrasounds were normal throughout the pregnancy, including a fetal anatomy survey. Both fetal MRI and fetal echocardiography were normal in the third trimester.
A baby girl was delivered via cesarean section at 39 0/7 weeks for non-reassuring fetal heart tracings after induction of labor. The NICU team was at the delivery, but the baby was well appearing and stable, with APGARS of 9/9. Decision was made to send the baby to the Well Newborn Nursery. Physical exam and vital signs were normal. During the hospitalization, she had a normal Head Ultrasound, Renal Ultrasound, and Echocardiogram. The baby breastfed well, lost minimal weight, was not jaundiced, passed newborn screening, and roomed in with her mothers entirely until discharge on day of life 4. At the time of this submission, she is a thriving 4-month-old. She continues to follow with Genetics, but no concerns have been identified.

Discussion: When a baby with a rare genetic diagnosis is born, there is a rush to decide what extra testing, if any, is needed in the immediate newborn period. On this baby’s admission, we searched PubMed for tetrasomy 18p and found 50 papers, mostly case reports. The presentations of chromosome 18 abnormalities were widely variable, with no correlation between prenatal screening results, neonatal complications, and long-term outcomes. There were many cases that ended in termination of pregnancy.

A Google search for tetrasomy 18p, however, led us to a website maintained by families of children with disorders of chromosome 18. It had a lengthy list of possible complications, but also suggestions for testing. We chose to follow these for lack of a plan with better evidence. We also found Facebook Groups for families of children with Chromosome 18 conditions, which offered both medical insights and social supports for parents.

Conclusions: With the rapid expansion of NIPT in pregnant women of all ages, unexpected genetic results will be diagnosed with increasing frequency. Until the outcomes are more clearly elucidated in the published medical literature, doctors and families alike will turn to the Internet as a way to aggregate the experiences of multiple patients. There are few guidelines about incorporating information found outside of the traditional peer reviewed and published literature, but there is powerful data to be gleaned in these non-traditional sources. As Pediatric Hospitalists take a larger role in Well Newborn Nurseries, we will be at the forefront of this medically and ethically challenging arena. More cases need to be published that show abnormal genetic testing can be compatible with a wide range of outcomes, including completely typical development. Centralized databases for rare genetic conditions will also be a powerful tool in helping families know what to expect in their children.

To cite this abstract:

Dossetter, BJ; Bennett, JA. What to Expect When You’re Expecting….a Baby with Tetrasomy 18. Abstract published at Hospital Medicine 2018; April 8-11; Orlando, Fla. Abstract 392. https://www.shmabstracts.com/abstract/what-to-expect-when-youre-expecting-a-baby-with-tetrasomy-18/. Accessed November 14, 2019.

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