Why ultrasound, not X-ray or MRI, became pregnancy's standard window
Obstetrics watches over pregnancy, birth and the weeks after, and it leans on one imaging tool above all. X-rays and CT carry radiation that can harm a developing foetus, MRI is too costly for routine checks, so ultrasound wins: no radiation, portable and live. Even so, the safety of frequent scanning has never been confirmed.
In some countries obstetrics is paired with gynaecology as a single surgical specialty, OB-GYN. Much of the work is screening. Early-pregnancy checks include blood tests for infections such as syphilis and an antibody test gauging the risk of haemolytic disease in the newborn, while Rh-negative mothers are given RhoGAM at 28 weeks to prevent Rh disease.
Genetic screening in the United States is shifting. The older AFP-quad test, taken around 16 to 18 weeks, looks at four blood markers. A newer integrated approach begins between 10 and 13 weeks with an ultrasound of the thickness of skin at the back of the foetal neck plus two blood chemicals, then refines the estimate with a second blood test later. It costs more but is quoted as detecting 93 percent of cases, against 88 percent for the older screen. Amniocentesis or chorionic villus sampling can supply a foetal karyotype when genetic disease is suspected.
Ultrasound does many jobs: dating the pregnancy, most accurately in the first trimester, counting foetuses and placentas, spotting ectopic pregnancy and, in the second trimester, checking for anomalies once structures are larger. Before week 6, age is judged from the diameter of the gestational sac; afterwards, from crown-rump length. Growing numbers of parents book extra scans with no medical purpose, such as 3D and 4D views.
Existing illnesses can interact with pregnancy. Diabetes raises risks including miscarriage and an oversized baby; lupus raises the chance of miscarriage and neonatal lupus; and thyroid problems can affect a child's early development. Pregnancy itself makes blood clot more readily, an adaptation against bleeding after birth. Preeclampsia, a dangerous rise in blood pressure, can appear after 20 weeks in women with no prior history. Severe persistent vomiting, hyperemesis gravidarum, has no confirmed cause, though a fast-rising placental hormone, HCG, is suspected.
Source: Obstetrics
