Second Trimester After IVF or IUI: When It Begins

You have crossed twelve weeks after IVF, IUI, or a long medicated road, and people are starting to say things like "you can relax now." You cannot, and that is not a flaw in you. If you are searching when do second trimester start, the honest answer is week 13 or 14 depending on which guideline you read. This post is a doctor-led map of what the second trimester actually looks like in the body and the mind for couples who arrived here the hard way.

The second trimester runs from roughly the start of week 14 through the end of week 27, depending on which professional body you ask. It is often described as the "easy" trimester because nausea typically lifts and energy returns. For couples who reached it after assisted conception, the experience is more layered. The body softens; the mind often does not. This post covers what is happening physically week by week, what the anatomy scan is actually for, and why pregnancy-specific anxiety can intensify rather than ease as the bump becomes visible.

When the second trimester actually starts and why definitions vary

The single most-searched question about this stage is when it starts. The honest answer is that two large professional bodies define it slightly differently, and that is where the "week 13 or 14" confusion in search comes from.

ACOG and most US clinicians define the second trimester as weeks 14 through 27, counting from the first day of the last menstrual period (LMP).¹ NICE and many UK clinicians use weeks 13 to 27, which shifts the start one week earlier. Both groups place the end of the trimester at 27 weeks and 6 days, with the third trimester beginning at 28 weeks 0 days. Practically, the difference is nominal. Nothing in your body changes on the calendar boundary.

After IVF, the calculation is more precise than LMP-dating. Gestational age is calculated from the embryo transfer date plus the embryo's age at transfer. A day-5 blastocyst transferred on May 1 is gestationally 2 weeks and 5 days on the day of transfer, and the LMP-equivalent EDD is set from that. If you are using a pregnancy app that asks for your LMP, double-check that the trimester boundaries align with the date your clinic gave you at transfer. They usually do, but app-derived dates can be off by a week.

The reason this matters is that several time-sensitive things hinge on the trimester boundary. The fetal anatomy scan is scheduled in a window (18 to 22 weeks). The first-trimester combined screening for chromosomal conditions closes at 13 weeks 6 days. The miscarriage risk numbers you have been clinging to drop substantially across these weeks, which is part of why the "you can relax now" pressure ramps up. After pregnancy after infertility (PAI), the calendar feels different. The week markers that family members celebrate often land harder for you, because each one is a milestone you spent years hoping for and are still afraid to lose.

What is happening in your body, week by week

Twelve to fourteen weeks of fairly continuous symptom change is a lot to track. Here is what to expect, broken into four-week blocks.

Weeks 13 to 16: Nausea typically lifts. Cohort data on pregnancy nausea consistently shows the majority of those affected reporting substantial improvement by week 14, though a minority continue into the second trimester. The uterus rises above the pubic bone, which is why you start to look noticeably pregnant rather than bloated. Round ligament pain (a sharp, brief pulling sensation low in the abdomen, often on movement) begins as the ligaments supporting the uterus stretch. Energy returns. Many people report sleeping better than they did at any point in the first trimester. Constipation often persists because progesterone is still slowing gut motility.

Weeks 17 to 20: Quickening, the first felt fetal movement, usually occurs in this window in first pregnancies, and earlier (sometimes from 15 to 16 weeks) in subsequent pregnancies. The placenta position becomes meaningful: anterior placentas cushion fetal movement and can delay perception by a couple of weeks, which is normal and not a problem. The fetal anatomy scan, which ACOG recommends between 18 and 22 weeks, is typically scheduled in this block.² The ISUOG international practice guidelines define the same window for the mid-trimester scan and standardise the views performed.⁴

Weeks 21 to 24: The viability threshold sits somewhere in this block, varying by NICU and by country. In the UK, the threshold for offering active resuscitation has shifted toward 22 weeks at experienced units. In the US, most units consider 23 to 24 weeks the practical viability boundary, with survival statistics rising sharply across these weeks. Fetal movement becomes more regular but is not yet predictable to a daily routine, and it can disappear for a few hours at a time, particularly when the fetus is in a deep-sleep cycle. Hearing a heartbeat at home with a personal doppler is unreliable in this window, and I do not recommend it; it produces false reassurance and false alarms in roughly equal measure.

Weeks 25 to 27: The glucose tolerance test (GTT, or OGTT in the UK) is scheduled, typically at 24 to 28 weeks. If you have PCOS or were on metformin pre-pregnancy, this window is when gestational diabetes is most likely to declare itself; the screen should not be skipped. The Tdap vaccine is recommended between 27 and 36 weeks per the CDC ACIP schedule, with earlier in the window preferred to maximise pertussis antibody transfer. Braxton-Hicks contractions (irregular, painless or mildly uncomfortable tightenings) may begin. They are not labour and do not indicate a problem.

The popular description of the second trimester as the "honeymoon trimester" is broadly true and individually variable. Most people do feel better. Some do not. If you have hyperemesis gravidarum, you may have ongoing nausea well into the second trimester. If you are managing a chronic condition (thyroid disease, autoimmune disease, depression), the second trimester is the window in which medication doses are reviewed and often adjusted upward as blood volume expands.

The anatomy scan and what they are actually looking for

The mid-trimester anatomy scan, scheduled between 18 and 22 weeks, is the single most clinically important appointment of the second trimester. It is also, for couples who came from infertility, the most loaded one emotionally. I want to lay out plainly what the scan covers so the experience is less of a black box.

The scan has two halves. The first is biometry: biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL). These are plotted on population growth curves. A baby measuring at the 30th percentile is not "behind"; the curve is wide. What sonographers and clinicians look for is the shape of the growth pattern, not a single number.

The second half is the systematic survey. The sonographer steps through a defined sequence: brain (cerebellum, ventricles, midline), face (lips, profile), heart (four chambers, then outflow tracts), and spine. Then abdominal wall, kidneys (both, plus the bladder), limbs, placenta location, cord vessels, and amniotic fluid volume. The ISUOG protocol is the international standard and is followed in nearly all units.⁴

Soft markers (echogenic intracardiac focus, choroid plexus cyst, isolated mild pyelectasis) are common, mostly benign findings whose significance depends on the prior screening results and the rest of the scan. A clear scan with one isolated soft marker is reassuring in most cases. Structural findings (a clear anomaly of one of the major systems) are different and warrant a referral to maternal-fetal medicine and often a follow-up detailed scan.

After IVF, the placenta position is worth specifically asking about, and whether you had a fresh or a frozen transfer is part of that conversation. A systematic review and meta-analysis by Vermey and colleagues found that singleton pregnancies conceived via ART have a modestly increased risk of placental anomalies. The anomalies include placenta previa, placental abruption, and placenta accreta spectrum, compared with non-ART singleton pregnancies.⁷ The absolute risks are still low. If the placenta is reported as low-lying or covering the cervix at the 20-week scan, your clinician will want to repeat the scan around 32 weeks to confirm whether it has migrated upward (most do).

You can ask to see what is on the screen. You can also ask not to be told the sex if you have not decided. You can request a written summary of the findings, which is often more useful than your memory of the conversation. If the scan is going on longer than expected, that is usually because a view was hard to get, not because something is wrong; ask if you would like to know.

The emotional shift no one prepared you for

The cultural script for the second trimester is calm. You "got past the danger zone." You can announce. You can buy a stroller. You can post the photo. For couples who came here through infertility or loss, none of those checkpoints feel as advertised, and the gap between the cultural script and your actual experience can be jarring.

Pregnancy-specific anxiety is its own construct in the perinatal mental health literature, distinct from generalised anxiety.⁶ It is characterised by persistent worry that focuses specifically on the pregnancy. The worry attaches to fetal viability, scan findings, fetal movement, and the perceived fragility of the pregnancy. It tends to dip in the early second trimester, the relative calm between the first ultrasound and the anatomy scan. The level rises again as the anatomy scan approaches, dips if the scan is reassuring, and rises once more in the third trimester. After a long TTC story, the baseline level of pregnancy-specific anxiety is higher than in spontaneously conceived pregnancies, and the dips are shallower.

The "I should feel grateful but I am still scared" loop is the most common version of this I see in clinic. It is not ingratitude. It is the cost of having spent months or years bracing for loss. The hypervigilance that protected you through the trying years does not switch off because the test was positive or the heartbeat was strong. The clinical name does not make it lighter, but it does make it real and treatable.

The other thing that often catches couples off guard is divergence. One partner may relax around the time of the anatomy scan; the other may not relax until the baby is home from hospital. Neither is the "right" timeline. The strain inside the couple is sometimes louder than the strain inside the body. Naming the divergence out loud, rather than waiting for the other person to catch up to your level of vigilance or calm, prevents weeks of silent friction.

The point at which pregnancy-specific anxiety crosses into clinical territory is when it is impairing function. You are not sleeping because you are checking for fetal movement. You are avoiding prenatal appointments, flooding ER triage, or the worry is bleeding into work and relationships in ways it did not before. ACOG Committee Opinion 757 recommends antenatal screening for depression and anxiety at least once during pregnancy using a validated tool such as the EPDS or GAD-7.⁵ If your clinic is not doing this at every visit, you can ask for it. I cover the specific decision around treatment, including SSRIs in pregnancy, in the PAI anxiety in later pregnancy post.

What is normal, and what is not

Most second-trimester symptoms are versions of the body adapting to expanded blood volume, a higher metabolic load, and a stretching uterus. The list that warrants a same-day call is short.

• Any vaginal bleeding, including spotting. Most second-trimester bleeding is benign (a cervical polyp, post-coital, a low placenta), but the assessment is done in person.
• Severe one-sided abdominal pain that does not settle with rest and position change. Round ligament pain is brief and pulling; persistent localised pain is different.
• Persistent severe headache, especially with visual changes (flashing lights, blurring, a curtain across vision). Preeclampsia risk rises after 20 weeks, and headache with visual change is the clinical pattern worth catching early.⁷
• Decreased fetal movement once you have established a regular pattern. Formal kick counting starts at 28 weeks per ACOG, but if you have been feeling daily movement and suddenly feel less, call.
• Sudden swelling of face or hands, or weight gain of more than 1 to 2 kg in a week. Generalised dependent swelling of the feet at end of day is normal; central swelling and rapid weight gain is not.
• Fever above 38°C (100.4°F). Treatable, but worth a call.
• Any fluid leak from the vagina that is not urine. Premature rupture of membranes (PPROM) before 37 weeks is uncommon but needs assessment.

The other thing I tell couples in clinic is that calling triage in the second trimester is not an overreaction. Triage exists for this. You do not need to apologise for using it.

What to ask before your next appointment

The visits in the second trimester are shorter than the first-trimester ones, and the agenda can fill quickly with the routine items. These are the questions worth bringing in writing.

• "Given my conception story, my history, and my age, what is my individualised risk for preterm birth, gestational diabetes, and preeclampsia, and what monitoring follows from that?"
• "Will I have additional growth scans in the third trimester, and on what cadence?"
• "What is the after-hours pathway if I am worried about movement or bleeding? Who do I call, and do I call before I come in?"
• "When are my Tdap, glucose tolerance test, and anti-D (if I am Rh-negative) scheduled?"
• "Do you screen for perinatal anxiety and depression at every visit, or only postpartum? Can I have a GAD-7 and EPDS now and again at 28 weeks?"

A good clinic will have answers to all of these. If your clinic is brusque or dismissive about the mental health questions, that is information about the unit, not about you.

What you can do this week

Concrete and proportionate.

1. Confirm your anatomy scan is scheduled in the 18 to 22 week window. If it is not, ask why. After IVF, this scan should not be missed or pushed.
2. If you wear a fitness tracker (Apple Watch, Garmin, Whoop), expect resting heart rate to rise by 10 to 20 bpm by mid-trimester. This is normal blood volume expansion, not a sign of something wrong. Tracker alerts about "abnormal" heart rate during pregnancy can be ignored after a single discussion with your clinician.
3. Do not start kick counts yet. ACOG recommends formal kick counting from 28 weeks.² Earlier counting creates false alarms, because fetal movement is not yet regular enough to count meaningfully. If you are checking constantly, you are feeding the anxiety, not the data.
4. Identify a perinatal mental health resource now, before you might need it. Postpartum Support International (US) operates a helpline at 1-800-944-4773, and PANDAS UK is on 0808 1961 776. Saving the number is not a commitment to using it; it is a small piece of practical preparation that often helps.
5. Have one conversation with your partner about where you each are. Not "are you excited," which is the wrong question. "How are you feeling about the anatomy scan?" or "What helps you, and what does not?" is the more useful one.

When to involve your clinician beyond the routine

• A scan finding (soft marker, growth shift, placental position) you want explained. Ask for a follow-up appointment specifically to discuss it, not on the call where you are told.
• Persistent anxiety that is disrupting sleep, function, or your relationship. This is treatable, and the second trimester is a reasonable window to start CBT or to discuss medication.
• A history of perinatal loss or trauma that is being reactivated by this pregnancy. Trauma-informed perinatal therapy is a specific resource and is different from general CBT.
• Any of the red flags listed above.

The second trimester is not a calm trimester for everyone who came here from infertility. Once you know roughly when do second trimester weeks start for your dating, the practical and emotional groundwork for the third trimester and a birth can be laid down. The work is not pretending the fear is gone. It is building a structure that lets you live alongside the fear without it running the day.

What's next

• If symptoms feel manageable and scans are reassuring: third trimester symptoms and what to watch for
• If anxiety is intensifying rather than easing: PAI anxiety in later pregnancy
• If you are starting to think about birth: writing a birth plan after IVF or IUI
• If something feels off or you have had bleeding: when things don't go to plan, second-trimester concerns

Sources

1. American College of Obstetricians and Gynecologists. Committee Opinion No. 700: Methods for Estimating the Due Date. Obstet Gynecol 2017;129(5):e150-e154 (Reaffirmed 2022). https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date
2. American College of Obstetricians and Gynecologists. Practice Bulletin No. 175: Ultrasound in Pregnancy. Obstet Gynecol 2016;128(6):e241-e256. https://www.acog.org/clinical/clinical-guidance/practice-bulletin/articles/2016/12/ultrasound-in-pregnancy
3. National Institute for Health and Care Excellence. Antenatal care. NICE guideline NG201. Published 2021, updated 2024. https://www.nice.org.uk/guidance/ng201
4. Salomon LJ, Alfirevic Z, Berghella V, et al. ISUOG Practice Guidelines (updated): performance of the routine mid-trimester fetal ultrasound scan. Ultrasound Obstet Gynecol 2022;59(6):840-856. https://obgyn.onlinelibrary.wiley.com/doi/10.1002/uog.24888
5. American College of Obstetricians and Gynecologists. Committee Opinion No. 757: Screening for Perinatal Depression. Obstet Gynecol 2018;132(5):e208-e212 (Reaffirmed 2023). https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2018/11/screening-for-perinatal-depression
6. Bayrampour H, Ali E, McNeil DA, Benzies K, MacQueen G, Tough S. Pregnancy-related anxiety: A concept analysis. Int J Nurs Stud 2016;55:115-130. https://www.sciencedirect.com/science/article/abs/pii/S0020748915003089
7. Vermey BG, Buchanan A, Chambers GM, et al. Are singleton pregnancies after assisted reproduction technology (ART) associated with a higher risk of placental anomalies compared with non-ART singleton pregnancies? A systematic review and meta-analysis. BJOG 2019;126(2):209-218. https://obgyn.onlinelibrary.wiley.com/doi/10.1111/1471-0528.15227