Testing in Pregnancy

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  • Testing
    • ELISA
      • Direct: An antigen is fixed onto a well, an enzyme-labelled antibody is added. If the antigen is present, a colour change will occur when a substrate solution is added.
      • Indirect: An antigen is fixed onto a well and a patient sample is added. If the patient has the antigen, antibodies to it will be in their sample and bind to the antigen of interest. The well is washed and an enzyme-labelled antibody is added, attaching to the primary antibody if it's there. A substrate solution is then added to produce a colour change or not.
      • Sandwich: A capture antibody is fixed onto a well, then antigens from a patient sample are added. An enzyme-labelled antibody that's specific to a different epitope of the patient's antigen is added. A substrate solution provides an indicative colour change.
      • Competitive: A capture antibody is fixed onto a well plate, then antigens from the patient sample are added, alongside a competitive inhibitor antigen that competes with the antigen of interest to bind to the capture. The well is rinsed out, then a secondary enzyme-labelled antibody is added. A substrate solution is added and the resulting colour change gives a measure of how much of the antigen of interest is in the patient sample.
      • Home Pregnancy Tests follow the principle of the sandwich ELISA. A patient urinates onto a stick, with any hCG in their urine binding to a fixed primary antibody. The stick is washed and incubated and as the hCG moves up the stick, it binds to a secondary antibody that binds to a different epitope, causing a colour change.
    • Scans
      • The dating scan screens for DS, ES, and PS with its combined (blood test and US scan) test, examining HCG, APPA, nucheal translucency, maternal age, BMI, and smoking status to calculate a risk of disability.
      • If a nucheal translucency wasn't taken at the dating scan, the quadruple test is offered at 14-20 weeks, only screening for DS. It tests for for f?hCG, inhibin A, unconjugated oestriol, and alphafetoprotein.
      • If the pregnancy is high risk, with a chance of developing a disability equal to or above 1 in 150, then invasive testing is offered.
        • Chorionic Villus Sampling - carried out 11-14 weeks - a needle is inserted transabdominally or transvaginally to collect a small tissue sample from the placenta for testing. Carries a miscarriage risk of up to 1%.
        • Amniocentesis - carried out between 15-20 weeks - a needle is inserted through the abdomen to collect a small sample of amniotic fluid. Carries a miscarriage risk of up to 1%.
        • The main non-invasive test is the NIPT, set to be rolled out across the NHS soon. It tests maternal blood with a fingerprick and examines the cell-free DNA the baby sheds into its mother's bloodstream. This is combined with maternal age and medical history to calculate a more reliable probability of developing a disability. While this test is non-invasive, it's not definitive; invasive testing is needed to reach a definite answer.
    • NHS Antenatal Care
      • 8-12 weeks: Booking Scan: Gives information on nutrition, diet, foetal development, pelvic and body exercises, antenatal care, classes, maternity benefits and changes in the body. The midwife gives care plan notes to a patient and sees if the mother needs any additional support. A history is taken to ideentify risk factors, vital stats are taken, screening is offered.
      • 8-14 weeks: Dating Scan is carried out to estimate due date, check physical development, and screen for conditions such as Down Syndrome.
      • approx. 16 weeks: information on the 20 week scan is given and it's offered. Results of prior scans are discussed, and vital stats are taken.
      • 18-20 weeks: the 20 week scan is carried out, screening for HIV, syphilis, and Hep B, and checking the physical development of the baby. The whooping cough vaccine is offered.
      • 25 weeks: first time mothers are given an extra appointment, in which, uterus size, blood pressure, and urine proteins are measured and tested.
      • 28 weeks: vital stats are taken, results of prior screenings are discussed.
      • 31 weeks: first time mothers are given another extra appointment where vital stats are taken.
      • 34 weeks: vital stats and uterus size are measured, more screening tests are offered, alongside anti-D treatment for Rh- mothers. Preparations for labour are made and the birth plan is finalised.
      • 36 weeks: an appointment where information on breastfeeding, new born care, vitamin K tests, postnatal health and depression is given. Vital stats are taken and external cephalic version is offered to rotate babies in breech position.
      • 38 weeks: vital stats are taken
      • 40 weeks: vital stats are taken, information on overdue pregnancies is given.
      • 41 weeks: vital stats are taken, a membrane sweep and induced labour are offered. If decline, a meeting happens next week and increased monitoring begins.

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