The aim of the project is to:

1. Investigate organ development and growth in fetuses with sex chromosome disorders;
2. Investigate growth, development, and morbidity in children with sex chromosome disorders during the first years of life;
3. Delineate how variations in sex chromosome number affect the epigenetic and genetic mechanisms regulating gene expression in the placenta and in multiple tissues of the child after birth over time during early childhood;
4. Investigate the gut microbiome in children with sex chromosome disorders during the first years of life;
5. Identify the epigenetic and genetic mechanisms and placental and child-specific alterations underlying the phenotype observed in fetuses, children, and adults with sex chromosome disorders, using a deep phenotyping approach.

Inclusion Criteria for pregnant participants in case group:

Age ≥18 years Fetus with a genetically verified sex chromosome disorder Written informed consent

Inclusion Criteria for pregnant participants in control group:

Age ≥18 years Normal first- and second-trimester ultrasound examinations Fetal growth within the normal range Written informed consent

Inclusion Criteria for mothers in the case group:

Age ≥18 years at the time of pregnancy with the child Child with a genetically verified sex chromosome disorder Written informed consent

Inclusion Criteria for mothers in the control group:

Age ≥18 years at the time of pregnancy with the child Normal first- and second-trimester ultrasound examinations during the pregnancy Normal fetal growth during the pregnancy Written informed consent

Inclusion Criteria for children in the case group:

If parents share joint custody, written informed consent must be obtained from both parents Ability to undergo a physical examination Child with a genetically verified sex chromosome disorder (prenatally or postnatally diagnosed)

Inclusion Criteria for children in the control group:

If parents share joint custody, written informed consent must be obtained from both parents Ability to undergo a physical examination

Exclusion Criteria for all groups:

Severe claustrophobia Implanted magnetic material contraindicating MRI

Recruitment of cases will take place at obstetric departments, departments of clinical genetics, and pediatric departments throughout Denmark.

Recruitment of controls will take place at the Department of Gynecology and Obstetrics and Department of Pediatrics, Aarhus University Hospital as well as via Facebook groups.