prenatal testing prenatal testing prenatal testing consists of prenatal screening and prenatal diagnosis, which are aspects of prenatal care that focus on detecting problems with the pregnancy as early as possible. these may be anatomic and physiologic problems with the health of the zygote, embryo, or fetus, either before gestation even starts (as in preimplantation genetic diagnosis) or as early in gestation as practicable. screening can detect problems such as neural tube defects, chromosome abnormalities, and gene mutations that would lead to genetic disorders and birth defects, such as spina bifida, cleft palate, down syndrome, tay–sachs disease, sickle cell anemia, thalassemia, cystic fibrosis, muscular dystrophy, and fragile x syndrome. some tests are designed to discover problems which primarily affect the health of the mother, such as papp-a to detect pre-eclampsia or glucose tolerance tests to diagnose gestational diabetes. screening can also detect anatomical defects such as hydrocephalus, anencephaly, heart defects, and amniotic band syndrome. an example of an algorithm for prenatal testing for chromosomal abnormalities. prenatal testingsynonymsprenatal screening, prenatal diagnosispurposedetecting problems with the pregnancy prenatal screening focuses on finding problems among a large population with affordable and noninvasive methods. prenatal diagnosis focuses on pursuing additional detailed information once a particular problem has been found, and can sometimes be more invasive. the most common screening procedures are routine ultrasounds, blood tests, and blood pressure measurement. common diagnosis procedures include amniocentesis and chorionic villus sampling. in some cases, the tests are administered to determine if the fetus will be aborted, though physicians and patients also find it useful to diagnose high-risk pregnancies early so that delivery can be scheduled in a tertiary care hospital where the baby can receive appropriate care. prenatal testing in recent years has been moving towards non-invasive methods to determine the fetal risk for genetic disorders. the rapid advancement of modern high-performance molecular technologies along with the discovery of cell-free fetal dna (cffdna) in maternal plasma has led to new methods for the determination of fetal chromosomal aneuploidies. this type of testing is referred to as non-invasive prenatal testing (nipt). invasive procedures remain important, though, especially for their diagnostic value in confirming positive non-invasive findings and detecting genetic disorders. purpose there are three purposes of prenatal diagnosis: (1) to enable timely medical or surgical treatment of a condition before or after birth, (2) to give the parents the chance to abort a fetus with the diagnosed condition, and (3) to give parents the chance to prepare psychologically, socially, financially, and medically for a baby with a health problem or disability, or for the likelihood of a stillbirth. prior information about problems in pregnancy means that healthcare staff as well as parents can better prepare themselves for the delivery of a child with a health problem. for example, down syndrome is associated with cardiac defects that may need intervention immediately upon birth. testing guidelines and qualifying risk factors for invasive testing the american college of obstetricians and gynecologists (acog) guidelines currently recommend that anyone who is pregnant, regardless of age, should discuss and be offered non-invasive prenatal genetic screening and diagnostic testing options. non-invasive prenatal genetic screening is typically performed at the end of the 1st trimester (11–14 weeks) or during the beginning of the second trimester (15–20 weeks) and involves the pregnant woman receiving a blood draw with a needle and a syringe, and an ultrasound of the fetus. screening tests can then include serum analyte screening or cell-free fetal dna, and nuchal translucency ultrasound , respectively. it is important to note that screening tests are not diagnostic, and concerning screening results should be followed up with invasive diagnostic testing for a confirmed diagnosis. invasive diagnostic prenatal genetic testing can involve chronic villus sampling (cvs) or amniocentesis. the acog recommends genetic screening before pregnancy to all pregnant women planning to have a family. after comprehensive counseling and discussion that acknowledges residual risks, it is important to respect the patients' right of choosing to pursue or not pursue any component of genetic testing. the following are some reasons why a woman might consider her risk of birth defects already to be high enough to warrant skipping screening and going straight for invasive testing. increased risk of fetal aneuploidy based on personal obstetric history or family history affected by aneuploidy increased risk for a known genetic or biochemical disease of the fetus maternal transmissible infectious disease such as rubella or toxoplasma parental request in the context of acute parental anxiety or under exceptional circumstances by invasiveness amniocentesis is an example of an invasive diagnostic prenatal test. diagnostic prenatal testing can be performed by invasive or non-invasive methods. an invasive method involves probes or needles being inserted into the uterus, e.g. amniocentesis, which can be done from about 14 weeks gestation, and usually up to about 20 weeks, and chorionic villus sampling, which can be done earlier (between 9.5 and 12.5 weeks gestation) but which may be slightly more risky to the fetus. one study comparing transabdominal chorionic villus sampling with second trimester amniocentesis found no significant difference in the total pregnancy loss between the two procedures. however, transcervical chorionic villus sampling carries a significantly higher risk, compared with a second-trimester amniocentesis, of total pregnancy loss (relative risk 1.40; 95% confidence interval 1.09 to 1.81) and spontaneous miscarriage (9.4% risk; relative risk 1.50; 95% confidence interval 1.07 to 2.11). ultrasonography is an example of a non-invasive diagnostic prenatal test. non-invasive techniques include examinations of the woman's womb through ultrasonography and maternal serum screens (i.e. alpha-fetoprotein). blood tests for select trisomies (down syndrome in the united states, down and edwards syndromes in china) based on detecting cell-free placental dna present in maternal blood, also known as non-invasive prenatal testing (nipt), have become available. if an elevated risk of chromosomal or genetic abnormality is indicated by a non-invasive screening test, a more invasive technique may be employed to gather more information. in the case of neural tube defects, a detailed ultrasound can non-invasively provide a definitive diagnosis. one of the major advantages of the non-invasive prenatal testing is that the chance of a false positive result is very low. this accuracy is very important for the pregnant woman, as due to a high sensitivity and specificity of the testing, especially for down syndrome, the invasive testing could be avoided, which includes the risk of a miscarriage. testing methods, by invasiveness invasiveness test comments time non-invasive preimplantation genetic diagnosis (pgd) during in vitro fertilization (ivf) procedures, it is possible to sample cells from human embryos before implantation. pgd is in itself non-invasive, but ivf usually involves invasive procedures such as transvaginal oocyte retrieval before implantation non-invasive external examination examination of the woman's uterus from outside the body. the uterus is commonly palpated to determine if there are problems with the position of the fetus (i.e. breech position). fundal height may also be measured. second or third trimester non-invasive ultrasound detection commonly dating scans (sometimes known as booking scans or dating ultrasounds) from 7 weeks to confirm pregnancy dates and look for multiple pregnancies. the specialised nuchal scan at 11–13 weeks may be used to identify higher risks of downs syndrome. later morphology scans, also called anatomy ultrasound, from 18 weeks may check for any abnormal development. additional ultrasounds may be performed if there are any other problems with the pregnancy, or if the pregnancy is post-due. first or second trimester non-invasive fetal heartbeat listening to the fetal heartbeat via an external monitor placed on the outside of the abdomen. first or second trimester non-invasive non-stress test use of cardiotocography during the third trimester to monitor fetal wellbeing. third trimester non-invasive maternal blood pressure used to screen for pre-eclampsia throughout the pregnancy. first, second and third trimester non-invasive maternal weighing unusually low or high maternal weight can indicate problems with the pregnancy. first, second and third trimesters. less invasive fetal cells in maternal blood (fcmb) requires a maternal blood draw. based on enrichment of fetal cells which circulate in maternal blood. since fetal cells hold all the genetic information of the developing fetus, they can be used to perform prenatal diagnosis. first trimester less invasive cell-free fetal dna in maternal blood requires a maternal blood draw. based on dna of fetal origin circulating in the maternal blood. testing can potentially identify fetal aneuploidy (available in the united states, beginning 2011) and gender of a fetus as early as six weeks into a pregnancy. fetal dna ranges from about 2–10% of the total dna in maternal blood. cell-free fetal dna also allows whole genome sequencing of the fetus, thus determining the complete dna sequence of every gene. first trimester less invasive glucose tolerance testing requires a maternal blood draw. used to screen for gestational diabetes. second trimester less invasive transcervical retrieval of trophoblast cells cervical mucus aspiration, cervical swabbing, and cervical or intrauterine lavage can be used to retrieve trophoblast cells for diagnostic purposes, including prenatal genetic analysis. success rates for retrieving fetal trophoblast cells vary from 40% to 90%. it can be used for fetal sex determination and identify aneuploidies. antibody markers have proven useful to select trophoblast cells for genetic analysis and to demonstrate that the abundance of recoverable trophoblast cells diminishes in abnormal gestations, such as in ectopic pregnancy or anembryonic gestation. first trimester less invasive maternal serum screening including β-hcg, papp-a, alpha fetoprotein, inhibin-a. first or second trimester more invasive chorionic villus sampling involves getting a sample of the chorionic villus and testing it. this can be done earlier than amniocentesis, but may have a higher risk of miscarriage, estimated at 1%. after 10 weeks more invasive amniocentesis this can be done once enough amniotic fluid has developed to sample. cells from the fetus will be floating in this fluid, and can be separated and tested. miscarriage risk of amniocentesis is commonly quoted as 0.06% (1:1600). by amniocentesis it is also possible to cryopreserve amniotic stem cells. after 15 weeks more invasive embryoscopy and fetoscopy though rarely done, these involve putting a probe into a women's uterus to observe (with a video camera), or to sample blood or tissue from the embryo or fetus. more invasive percutaneous umbilical cord blood sampling pubs is a diagnostic genetic test that examines blood from the fetal umbilical cord to detect fetal abnormalities. 24–34 weeks by pregnancy stage pre-conception prior to conception, couples may elect to have genetic testing done to determine the odds of conceiving a child with a known genetic anomaly. the most common in the caucasian population are: cystic fibrosis fragile x syndrome blood disorders such as sickle cell disease tay-sachs disease spinal muscular atrophy hundreds of additional conditions are known and more discovered on a regular basis. however the economic justification for population-wide testing of all known conditions is not well supported, particularly once the cost of possible false positive results and concomitant follow-up testing are taken into account. there are also ethical concerns related to this or any type of genetic testing. one or both partners may be aware of other family members with these diseases. testing prior to conception may alleviate concern, prepare the couple for the potential short- or long-term consequences of having a child with the disease, direct the couple toward adoption or foster parenting, or prompt for preimplantation genetic testing during in vitro fertilization. if a genetic disorder is found, professional genetic counseling is usually recommended owing to the host of ethical considerations related to subsequent decisions for the partners and potential impact on their extended families. most, but not all, of these diseases follow mendelian inheritance patterns. fragile x syndrome is related to expansion of certain repeated dna segments and may change generation-to-generation. first trimester at early presentation of pregnancy at around 6 weeks, early dating ultrasound scan may be offered to help confirm the gestational age of the embryo and check for a single or twin pregnancy, but such a scan is unable to detect common abnormalities. details of prenatal screening and testing options may be provided. around weeks 11–13, nuchal translucency scan (nt) may be offered which can be combined with blood tests for papp-a and beta-hcg, two serum markers that correlate with chromosomal abnormalities, in what is called the first trimester combined test. the results of the blood test are then combined with the nt ultrasound measurements, maternal age, and gestational