Pregnancy tests and scans: the full trimester-by-trimester schedule

Why these tests matter beyond routine check-boxes

Pregnancy is a normal physiological process, but it places the body under exceptional demands, and several of the most dangerous complications begin with no symptoms at all. Preeclampsia, for example, affects between 5% and 10% of pregnancies worldwide and is a leading cause of maternal death in low- and middle-income countries, yet it often causes no pain until it becomes severe. Routine blood pressure measurement and urine protein testing are the only way to catch it early.

Prenatal investigations divide into two categories: blood tests that measure markers in the mother, and ultrasound scans that monitor the baby directly. Both are necessary. A perfect scan does not replace a blood panel, and a normal blood panel does not tell you whether the baby's heart has formed correctly.

The World Health Organization recommends a minimum of eight antenatal care contacts during pregnancy, with four of them in the first half. In practice across the Arab world, particularly in rural areas, active conflict zones, or countries with overstretched health systems, this is not always achieved. Knowing which tests matter most, and when their windows close, puts you in a better position to advocate for yourself.

First trimester tests: weeks 1 to 13

The first test most women need is a blood Beta-hCG measurement to confirm pregnancy and give an accurate gestational age, which is more precise than a home urine test in the very early weeks. If you have abdominal pain alongside a positive test, this same measurement may be repeated to check whether the value is rising normally, because an ectopic pregnancy often produces a slowly rising or plateauing hCG rather than the expected doubling every 48 to 72 hours.

Around week six a first dating ultrasound confirms the pregnancy is inside the uterus, identifies a heartbeat, and establishes the due date. This scan is especially important if you have any pelvic pain or light bleeding, since those symptoms can signal an ectopic implantation which is a medical emergency.

Between weeks 11 and 13, the combined first-trimester screening takes place. This pairs a nuchal translucency (NT) ultrasound measurement (the fluid thickness behind the baby's neck) with two blood markers: PAPP-A and free Beta-hCG. Together they produce a probability estimate for chromosomal conditions including Down syndrome. A 2025 systematic review and meta-analysis confirmed that increased NT thickness is associated with a wide range of adverse fetal outcomes beyond trisomy 21, reinforcing the value of this measurement even when chromosome results are normal.

The first trimester also carries a full blood panel. Blood group and Rhesus factor matter because a Rhesus-negative mother carrying a Rhesus-positive baby needs a protective Anti-D injection at specific points. A full blood count (CBC) screens for early anaemia, which is very common regionally. Fasting blood glucose, thyroid function (TSH), liver and kidney markers, and infectious disease serology (hepatitis B surface antigen, rubella IgG, syphilis, HIV, and often toxoplasmosis) are tested at this first visit.

What a first-trimester chromosomal screening result actually means

A first-trimester screening result is a probability estimate, not a diagnosis. It might say your risk of Down syndrome is 1 in 200. That does not mean your baby has Down syndrome. It means that among pregnancies with the same combination of measurements, approximately one in 200 would be affected. The result tells you whether further testing is warranted, not whether there is a problem.

If the probability is above the threshold your hospital uses (commonly around 1:150 or 1:250, though this varies), you will be offered cell-free fetal DNA testing, known as NIPT. This is a blood test from the mother that analyses fragments of the baby's DNA circulating in her blood. It has high sensitivity and specificity for the common chromosomal trisomies, but it is not available in all hospitals across the region and carries a significant out-of-pocket cost in most countries. The definitive diagnostic alternatives are chorionic villus sampling (CVS) in the first trimester or amniocentesis in the second, both of which carry a small procedural risk.

A normal first-trimester screening result does not guarantee that the baby is unaffected. It significantly lowers the probability of the screened conditions, but it does not screen for every possible chromosome or structural problem. The anatomy scan in the second trimester completes a different part of the picture.

Second trimester tests: weeks 14 to 27

The anatomy scan, sometimes called the anomaly scan or morphology scan, is the most detailed structural examination of the pregnancy. Performed between weeks 18 and 22, it examines the baby's brain, face, spine, heart, abdominal organs, limbs, and placental position, as well as amniotic fluid volume. This window matters: after week 24 the baby's size makes complete imaging significantly harder, and the scan loses some of its diagnostic reach. The FIGO 2019 initiative on first-trimester screening specifically underscores how timing of detailed fetal assessment affects detection rates.

Between weeks 24 and 28, every pregnant woman should have an oral glucose tolerance test (OGTT) to screen for gestational diabetes. This test is particularly important in the Arab world. A 2021 systematic review and meta-analysis covering the Middle East and North Africa found that gestational diabetes prevalence in the region is among the highest globally, driven by high rates of obesity, older maternal age at pregnancy, and underlying insulin resistance. A separate 2022 UAE cohort study applying multiple diagnostic criteria found substantial variation in gestational diabetes rates depending on which threshold is used, highlighting the importance of understanding which criteria your hospital follows.

Throughout the second trimester, blood pressure is measured at every visit and urinalysis checks for protein. If anaemia was found in the first trimester, a repeat CBC confirms whether iron supplementation has worked. In higher-risk pregnancies, a Doppler ultrasound assessing blood flow through the umbilical cord and the uterine arteries may be added from around week 20.

Third trimester tests: week 28 to delivery

At week 28, every Rhesus-negative woman carrying a baby who may be Rhesus-positive receives an Anti-D injection. This immunoglobulin prevents sensitisation if fetal blood cells have crossed into the maternal circulation, which can happen even without visible bleeding. Sensitisation matters because in a subsequent Rhesus-positive pregnancy, the antibodies already formed can cross the placenta and attack the baby's red blood cells. Anti-D availability is uneven across the region, so ask about it proactively at your first antenatal visit.

Between weeks 35 and 37, a Group B Streptococcus (GBS) swab is taken from the vagina and rectum. This bacterium colonises around 20% of women without causing any symptoms in the mother, but it can cause serious infection in a newborn during delivery. A positive result means intravenous antibiotics during labour, which is very effective at preventing neonatal infection. The swab is routinely offered in most Gulf country hospitals but less consistently in other parts of the region.

Growth scans every three to four weeks from around week 28 onwards track the baby's estimated weight and amniotic fluid levels. A repeat full blood count confirms your haemoglobin before delivery. Cardiotocography (CTG), continuous or intermittent monitoring of the fetal heart rate, is added when risk factors are present. In areas where toxoplasmosis is common, such as parts of the Levant and North Africa where raw or undercooked meat is consumed and cat contact is frequent, antibody testing may be repeated in the third trimester if the first-trimester result was negative.

Reading your full blood count results in pregnancy

Anaemia is the most common abnormal blood result in pregnancy across the Arab world. The WHO defines anaemia in pregnancy as haemoglobin below 11 g/dL in the first and third trimesters, and below 10.5 g/dL in the second. Iron deficiency is by far the most common cause, and it shows up as low serum iron and ferritin alongside high TIBC (total iron binding capacity). The haemoglobin alone can appear borderline while ferritin is very low, which is why ferritin is worth checking separately.

Your platelet count in the CBC is also watched carefully. A sharp drop in platelets during pregnancy can signal dangerous conditions including severe preeclampsia or HELLP syndrome (haemolysis, elevated liver enzymes, and low platelet count). If your platelet count drops below 100,000 per cubic millimetre in the third trimester, your doctor needs to know immediately.

Liver enzyme results, when added to the panel, complete the picture for HELLP syndrome. Rising ALT and AST alongside falling platelets and rising blood pressure form a triad that makes HELLP the most likely explanation. This is a true obstetric emergency that requires delivery, regardless of gestational age.

When tests are not available: how to prioritise

Several tests that are standard in Europe and North America are unavailable in parts of the Arab world, or carry significant out-of-pocket costs. NIPT, for example, costs between 300 and 600 dollars or more in most regional private facilities and is rarely covered by public insurance. A thorough anatomy scan performed by an experienced sonographer can still detect many structural abnormalities even when NIPT is unavailable.

If full access to every test listed here is not realistic in your setting, the following three have fixed windows that make them highest priority: the nuchal translucency scan between weeks 11 and 13, the anatomy scan between weeks 18 and 22, and the glucose tolerance test between weeks 24 and 28. Missing these windows means the specific diagnostic value of those tests is lost.

Where continuous specialist care is difficult to access, knowing which symptoms require urgent evaluation rather than a scheduled appointment is equally important. This is not a substitute for regular antenatal visits, but it is a meaningful safety layer.

Practical tips for keeping track of your results

Keep a personal copy of every test result. In most hospitals across the Arab world there is no unified electronic record that follows you between facilities. If you change your doctor, move to another city, or are referred to a specialist, you may find yourself starting from scratch. A small notebook dedicated to the pregnancy, or a notes app on your phone, is enough. Write down the date, the test name, the value, and the reference range given by the lab.

This matters more than it may seem. Two different labs may use slightly different reference ranges for the same test, so knowing your actual number allows you to ask meaningful questions rather than simply being told normal or abnormal. A haemoglobin of 10.8 g/dL is below the first-trimester WHO threshold but above some local lab thresholds, and the difference in how it is communicated to you depends on which reference range the lab prints.

If you have risk factors, including pre-existing diabetes, high blood pressure, a previous pregnancy loss, twins, or a family history of genetic conditions, your schedule will differ from the standard low-risk one described here. The tests listed in this article represent the baseline for a straightforward single pregnancy. Ask your doctor at the first visit whether additional tests apply to your situation.

When to seek urgent assessment outside a scheduled visit

Some symptoms during pregnancy require immediate evaluation rather than waiting for a scheduled appointment. Knowing these signs in advance, before a problem develops, is part of safe antenatal care. The earlier a dangerous complication is identified, the wider the range of interventions available.

A severe headache that is unusual for you, particularly if accompanied by visual disturbance such as blurring or flashing lights, or by right upper abdominal pain, may indicate severe preeclampsia or early HELLP syndrome. Blood pressure measurement in any clinic or pharmacy is enough to determine whether urgent hospital assessment is needed.

Sudden swelling of the hands, face, or eyes (as opposed to the gradual ankle swelling that is common in late pregnancy), any vaginal bleeding at any stage of pregnancy, a marked reduction in fetal movements compared with your normal pattern, and a fever with body aches all warrant same-day evaluation rather than waiting.

Sources

• Poon LC, Shennan A, Hyett JA et al: The International Federation of Gynecology and Obstetrics (FIGO) initiative on pre-eclampsia: A pragmatic guide for first-trimester screening and prevention, International journal of gynaecology and obstetrics, 2019
• Suciu I, Galeva S, Abdel Azim S et al: First-trimester screening-biomarkers and cell-free DNA, The journal of maternal-fetal and neonatal medicine, 2021
• Paquet C, Yudin MH, Society of Obstetricians and Gynaecologists of Canada et al: Toxoplasmosis in pregnancy: prevention, screening, and treatment, Journal of obstetrics and gynaecology Canada, 2013
• World Health Organization: WHO recommendations on antenatal care for a positive pregnancy experience
• Al-Rifai RH, Aziz F: Prevalence of type 2 diabetes, prediabetes, and gestational diabetes mellitus in women of childbearing age in Middle East and North Africa, 2000-2017: protocol for two systematic reviews and meta-analyses, Systematic reviews, 2018
• Matarrelli B, Khalil A, Bernassola M et al: Outcome of fetuses with early increased nuchal translucency: systematic review and meta-analysis, Ultrasound in obstetrics and gynecology, 2025