Small for Gestational Age at Delivery

This basket trial will enroll prepubertal children and adolescents with clinically diagnosed and genetically confirmed (if applicable) TS, SHOX-D, SGA, or ISS between ages of ≥2 and \<18 years with open growth plates. The purpose of the study is to see how well treatment with once-weekly lonapegsomatropin works compared to treatment with daily somatropin. Approximately 186 participants will be distributed equally (1:1), to receive either lonapegsomatropin for 2 years or somatropin for 1 year followed by lonapegsomatropin for 1 year. This trial will be conducted in the United States, France, Germany, Italy, Romania, Spain and South Korea.

The goal of this clinical trial is to learn more about how the food and nutrition babies receive while in the Neonatal Intensive Care Unit (NICU) influences their ability to gain weight and fat-free mass, and their future growth and development. Participants will: * have body growth measurements collected using the PEAPOD device * have nutritional information collected, and * be followed for neurodevelopmental outcomes Participants can expect to be in the study for 36 months.

The overall aim of the study is to evaluate the prevalence of motor- and neurological disorders (cerebral pares and other less severe motor disorders) in Swedish infants with a high-risk neonatal period and to elucidate whether these children receive motor related health care (MRHC) at 2 and or 5,5 years of age.

Babies may be born appropriately grown for gestational age (AGA, \>10th centile) or small for gestational age (SGA, \<10th centile). Babies who are SGA and have evidence in utero of vascular compromise using antenatal doppler indices are classified as having fetal growth restriction (FGR). Babies with FGR are at increased risk of cardiovascular disease in adult life. Increased arterial stiffness and intima-media thickness are thought to mediate this risk in adults. It is not known how early in life these changes can be robustly detected. In addition, very little is known generally about how babies' hearts and arteries change in structure and function over the first year of life, whether affected by SGA or not. This study aims to understand if there are differences in cardiac and arterial structure and function between babies born AGA or SGA. Within the group of SGA babies, the study team will investigate whether FGR and maternal pre-eclampsia influence these measurements. The effects gestational age on these parameters will be studied within all groups: half of the babies recruited will be \<32 weeks gestational age (GA), and half will be ≥32 weeks GA. Study participants will have further measurements at 3-6 months of life to assess if cardiac and arterial structure and function change in babies over the first year of life. The study team will use the Vicorder device to measure arterial stiffness, and assess the feasibility of using this device in neonates. The Vicorder will also be used to measure cardiac output. The feasibility and validity of this device for this purpose will be investigated (Vicorder is not validated for cardiac output measurement in infants). Vicorder cardiac output results will be compared to echocardiography and bioimpedence technology (using the NICaS monitor). The study team will use ultrasound for arterial structure measurements of the carotid artery and aorta.