Editing Obstetrics (section)

==== Fetal assessments ====
[[Image:Scan12weeks.jpg|thumb|A dating [[Obstetric ultrasonography|scan]] at 12 weeks]]
[[Obstetric ultrasonography]] is routinely used for dating the gestational age of a pregnancy from the size of the [[fetus]], determine the number of fetuses and [[placenta]]e, evaluate for an [[ectopic pregnancy]] and first trimester bleeding, the most accurate dating being in first trimester before the growth of the foetus has been significantly influenced by other factors.<ref>{{Cite journal | vauthors = Kansky C, Ramus RM |date=2021-06-15 | veditors = Pierce Jr JG |title=Basic Obstetric Ultrasound: Background, Indications, Contraindications |url=https://emedicine.medscape.com/article/2047305-overview | journal = Medscape }}</ref> Ultrasound is also used for detecting congenital anomalies (or other foetal anomalies) and determining the [[biophysical profile]]s (BPP), which are generally easier to detect in the second trimester when the foetal structures are larger and more developed.<ref>{{cite book | vauthors = DeFrancesco V | chapter = Perinatology. | title = Clinical Engineering Handbook | date = January 2004 | pages = 410–416 | publisher = Academic Press| doi = 10.1016/B978-012226570-9/50102-2 | isbn = 978-0-12-226570-9 }}</ref>

[[X-ray]]s and [[computerized tomography]] (CT) are not used, especially in the first trimester, due to the [[ionizing radiation]], which has [[teratogen]]ic effects on the foetus.<ref>{{cite journal | vauthors = Shaw P, Duncan A, Vouyouka A, Ozsvath K | title = Radiation exposure and pregnancy | journal = Journal of Vascular Surgery | volume = 53 | issue = 1 Suppl | pages = 28S–34S | date = January 2011 | pmid = 20869193 | doi = 10.1016/j.jvs.2010.05.140 | series = Radiation Safety in Vascular Surgery | doi-access = free }}</ref> No effects of [[magnetic resonance imaging]] (MRI) on the foetus have been demonstrated,<ref>{{cite journal | vauthors = Alorainy IA, Albadr FB, Abujamea AH | title = Attitude towards MRI safety during pregnancy | journal = Annals of Saudi Medicine | volume = 26 | issue = 4 | pages = 306–309 | year = 2006 | pmid = 16885635 | pmc = 6074503 | doi = 10.5144/0256-4947.2006.306 }}</ref> but this technique is too expensive for routine observation. Instead, [[obstetric ultrasonography]] is the imaging method of choice in the first trimester and throughout the pregnancy, because it emits no [[radiation]], is portable, and allows for realtime imaging.<ref>{{cite book | vauthors = Herbst MK, Tafti D, Shanahan MM | chapter =Obstetric Ultrasound |date=2022 | chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK470450/ | title = StatPearls |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=29261880 |access-date=2022-04-29 }}</ref>

The safety of frequent ultrasound scanning has not been confirmed. Despite this, increasing numbers of women are choosing to have additional scans for no medical purpose, such as gender scans, 3D and 4D scans.<ref>{{cite journal | vauthors = Edvardsson K, Small R, Persson M, Lalos A, Mogren I | title = 'Ultrasound is an invaluable third eye, but it can't see everything': a qualitative study with obstetricians in Australia | journal = BMC Pregnancy and Childbirth | volume = 14 | issue = 1 | pages = 363 | date = October 2014 | pmid = 25336335 | pmc = 4287579 | doi = 10.1186/1471-2393-14-363 | doi-access = free }}</ref> A normal gestation would reveal a [[gestational sac]], [[yolk sac]], and [[fetal pole]].<ref>{{cite book | chapter = Obstetric Imaging | veditors = Weissleder R, Harisinghani MG, Wittenberg J, Chen JW |title=Primer of Diagnostic Imagin |date=2011 | pages = 533–574 |publisher=Mosby |location=St. Louis, Mo. |isbn=978-0-323-06538-2 |edition=5th | doi = 10.1016/B978-0-323-06538-2.00010-X }}</ref>

The [[Gestational age (obstetrics)|gestational age]] can be assessed by evaluating the mean gestational sac diameter (MGD) before week 6, and the crown-rump length after week 6. [[Multiple gestation]] is evaluated by the number of [[placenta]]e and [[amniotic sac]]s present.<ref>{{Cite web | vauthors = Khan AN, Sabih D, Sabih A |date=2021-04-26 |title=Early Pregnancy Loss (Embryonic Demise) Imaging: Practice Essentials, Ultrasonography |url=https://emedicine.medscape.com/article/403208-overview}}</ref>

Other tools used for assessment include:
* Fetal screening is used to help assess the viability of the fetus, as well as congenital abnormalities.<ref>{{Cite journal | vauthors = Marino T | veditors = Ramus RM |date=2021-06-14 |title=Prenatal Diagnosis for Congenital Malformations and Genetic Disorders: Practice Essentials, Noninvasive Techniques, Invasive Techniques |url=https://emedicine.medscape.com/article/1200683-overview | journal = Medscape }}</ref>
* Fetal [[karyotype]] can be used for the screening of genetic diseases. This can be obtained via [[amniocentesis]] or [[chorionic villus sampling]] (CVS<ref>{{Cite web |title=Chorionic villus sampling - Mayo Clinic |url=https://www.mayoclinic.org/tests-procedures/chorionic-villus-sampling/about/pac-20393533 |access-date=2022-04-29 |website=www.mayoclinic.org}}</ref>)
* Foetal [[haematocrit]] for the assessment of foetal [[anemia]], Rh isoimmunization, or [[hydrops fetalis|hydrops]] can be determined by [[percutaneous umbilical blood sampling]] (PUBS), which is done by placing a needle through the abdomen into the [[uterus]] and taking a portion of the [[umbilical cord]].<ref>{{cite book | vauthors = Gomella TL, Cunningham MD, Eyal FG, Tuttle DJ |title=Fetal Assessment |date=2013 |url=http://accesspediatrics.mhmedical.com/content.aspx?aid=1107523894 |work=Neonatology: Management, Procedures, On-Call Problems, Diseases, and Drugs |edition=7 |place=New York, NY |publisher=McGraw-Hill Education |access-date=2022-04-29 }}</ref>
* Fetal lung maturity is associated with how much [[surfactant]] the fetus is producing. Reduced production of surfactant indicates decreased lung maturity and is a high risk factor for [[infant respiratory distress syndrome]].<ref>{{cite book | vauthors = Jobe AH | chapter = Fetal lung maturation and the respiratory distress syndrome. | title = Fetal Physiology and Medicine | edition = Second | date = January 1984 | pages = 317–351 | publisher = Butterworth-Heinemann | doi = 10.1016/B978-0-407-00366-8.50016-2 | isbn = 978-0-407-00366-8 }}</ref> Typically a [[lecithin]]:[[sphingomyelin]] ratio greater than 1.5 is associated with increased lung maturity.
* [[Nonstress test]] (NST) for fetal heart rate<ref>{{Cite web |title=Nonstress test - Mayo Clinic |url=https://www.mayoclinic.org/tests-procedures/nonstress-test/about/pac-20384577 |access-date=2022-04-29 |website=www.mayoclinic.org}}</ref>
* [[Oxytocin challenge test]]