IVF Twins: A Week-by-Week Guide to Managing a Twin Pregnancy

An IVF twin pregnancy turns on one variable: whether the two babies share a placenta. Dichorionic twins are scanned about every four weeks and usually born at 37–38 weeks; monochorionic twins every two weeks from 16 weeks, with birth offered from 36.

This guide was compiled by the ProIVF Medical Editorial Team from RCOG Green-top Guideline No. 51, Society for Maternal-Fetal Medicine (SMFM) checklists and PubMed cohorts, and reviewed by the ProIVF Medical Advisory Board. It explains monitoring pathways, not personal risk.

Chorionicity sets your plan, not the number of embryos transferred

Your pathway branches at 11–14 weeks, when the sonographer records placenta and sac counts.

Two embryos transferred does not mean two placentas; one embryo does not mean one placenta. RCOG Green-top Guideline No. 51 (2017) puts about 30% of UK twin pregnancies as monochorionic, and 70% of monozygotic twins are monochorionic.

Rule of thumb:

• Two embryos → both implant: almost always dichorionic diamniotic (Di-Di): two placentas, two sacs, no shared circulation.
• One embryo → splits: usually monochorionic, one placenta, connected circulations.
• A boy and a girl on scan: proves dichorionicity.

Shared-placenta complications such as twin-to-twin transfusion syndrome need connected circulations, so they cannot occur in Di-Di twins. See chances of twins with IVF for twin rates by transfer strategy.

When can the scan tell me whether my twins share a placenta?

Chorionicity is best determined between 11+0 and 13+6 weeks, earlier the better. The sonographer reads the dividing membrane: dichorionic twins have a thick membrane with a wedge of placental tissue at its base (the “lambda” sign), while monochorionic twins have one thin membrane set at right angles to the placenta (the “T-sign”).

After about 14 weeks the answer gets harder: placentas merge, the membrane thins and an anterior placenta hides the lambda sign, so a mid-trimester scan may miss it. If your first scan did not record chorionicity, ask for the 7–8 week sac count and membrane description; where it cannot be established, most units manage you as monochorionic.

No blood test fills this gap: twin and singleton β-hCG ranges overlap so heavily that no number confirms twins, let alone placentation (twin hCG levels after IVF). The due date calculation from IVF guide converts transfer day and embryo age into these scan weeks.

The three twin types and what each costs in monitoring

Mo-Mo pairs are the rarest and hardest-watched: RCOG puts them at about 1% of monochorionic pairs, and a retrospective series of 30 Mo-Mo pairs reported total survival of 60%.

Sharing one sac removes the two-pocket fluid comparison that screens Mo-Di pairs and leaves no membrane to hold the cords apart: entanglement shows on Doppler in almost every case, so daily movement counting and inpatient cardiotocography become routine.

Appointments: Di-Di means 6–8 growth scans; Mo-Di adds 11–13 extra 30–45 minute visits plus a fetal medicine referral.

Your scan schedule by chorionicity

Dichorionic twins follow a growth-surveillance calendar; monochorionic twins a complication-detection calendar.

Dichorionic twins: the growth calendar

• 11+0–13+6 weeks: chorionicity, nuchal translucency, combined screening.
• 18–20+6 weeks: detailed anomaly scan.
• From about 20 weeks: growth scan every 4 weeks, both estimated fetal weights and amniotic fluid.
• From 34–36 weeks: timing and mode of birth discussed.

Monochorionic diamniotic twins: the two-weekly calendar

• 16+0 weeks onward: ultrasound every 2 weeks until birth, however uncomplicated.
• At every visit: deepest vertical pocket in each sac, umbilical artery pulsatility index, both fetal bladders, and from 16 weeks both estimated fetal weights and their difference.
• On indication: middle cerebral artery peak systolic velocity for anemia.

RCOG grades the rule level D but keeps it: TTTS risk runs to delivery, not just to 26 weeks. The 2026 SMFM checklist confirms that calendar, adds monthly growth checks, and sets birth at 34+0–37+6 weeks for uncomplicated Mo-Di pairs.

Do IVF twins have more complications than naturally conceived twins?

Yes for preterm birth, cesarean delivery, gestational diabetes and hypertension; no for the monochorionic-specific complications.

A 2024 meta-analysis of 111 cohort studies covering 802,462 twin pregnancies compared ART with naturally conceived twins (Hum Reprod Update 2024):

The last row is counterintuitive: IVF twins have roughly half the odds of TTTS, because most are dichorionic and cannot develop it.

The four monochorionic complications that cannot happen in Di-Di twins

If your report says dichorionic, you can stop reading here.

Twin-to-twin transfusion syndrome (TTTS)

TTTS complicates up to 15% of monochorionic pregnancies, per RCOG.

Diagnosis is by fluid discordance, not size: deepest vertical pocket below 2 cm in one sac with more than 8 cm in the other before 20 weeks, or more than 10 cm after 20 weeks.

How TTTS is staged and treated

Quintero staging drives counseling: I fluid discordance only, normal Doppler; II donor bladder not visible; III critically abnormal Doppler in either twin; IV hydrops or fluid around the hearts; V one or both twins dead.

Fetoscopic laser in a German series of 200 TTTS pregnancies left at least one survivor in 93% of stage I, 83% of II, 83% of III and 70% of IV cases. A Western Australian cohort of 71 women treated with amnioreduction or septostomy showed the same gradient: stage I delivered at a mean 32 weeks with 77% survival, stage IV at 27 weeks with 44%. Stage alone predicts little: 28% improved, 35% worsened, 37% stayed at the same grade, and progression sometimes skipped a stage.

“Women with monochorionic twins should have timing of birth discussed and be offered elective delivery from 36+0 weeks with the administration of antenatal steroids, unless there is an indication to deliver earlier.” — RCOG Green-top Guideline No. 51, Management of Monochorionic Twin Pregnancy, 2017 (recommendation grade C)

Selective fetal growth restriction (sGR)

Estimated fetal weight discordance above 20% defines sGR, affecting about 10–15% of monochorionic twins without TTTS and over 50% once TTTS is present.

Umbilical artery Doppler splits it into three types that set the delivery week:

• Type I (normal or positive end-diastolic flow): more than 90% perinatal survival; delivery at 34–36 weeks.
• Types II and III (absent or reversed end-diastolic flow): delivery by 32 weeks unless growth or Doppler deteriorates.
• sGR carries up to a 29% risk of intrauterine demise of the smaller twin.

Reversed ductus venosus flow triggers consideration of delivery (RCOG grade B).

Twin anemia-polycythemia sequence (TAPS)

TAPS moves quietly: small artery-to-artery channels shift red cells, not fluid, so amniotic fluid stays normal.

It occurs spontaneously in up to 2% of uncomplicated Mo-Di twins and in up to 13% of monochorionic pregnancies after fetoscopic laser ablation, where recurrent TTTS reaches up to 14%; RCOG screens with middle cerebral artery peak systolic velocity after laser and in complicated pairs.

Single twin demise

The hardest number in monochorionic counseling: after one twin dies, RCOG puts the survivor’s death risk at about 15% and neurological abnormality at about 26%. Such pairs go to a fetal medicine center; brain MRI follows about 4 weeks later and middle cerebral artery Doppler monitors the survivor for anemia.

When should twins be delivered? The evidence behind 36, 37 and 38 weeks

Uncomplicated dichorionic twins are offered birth from 37 weeks; uncomplicated monochorionic diamniotic twins from 36.

In a cohort of 697 uncomplicated twin pregnancies delivering at or beyond 35 weeks (171 monochorionic, 526 dichorionic), neonatal composite morbidity fell as gestation advanced, bottoming out at 38 weeks for monochorionic and 39 weeks or more for dichorionic twins. At 36 weeks (monochorionic) and 37 weeks (dichorionic), delivering and waiting carried the same morbidity — the source of the recommendation (Obstet Gynecol Sci 2016).

Antenatal steroids matter more for twins than singletons, since most arrive before 39 weeks; RCOG advises them when birth is expected within 7 days.

Can you deliver twins vaginally? The trial that randomized 2,804 women

Yes: if both twins present head-down and nothing else mandates a section, planned vaginal birth is the evidence-supported default.

The Twin Birth Study randomized 2,804 women between 32+0 and 38+6 weeks with the leading twin head-down to planned cesarean or planned vaginal delivery (N Engl J Med 2013).

The composite outcome odds ratio with planned cesarean was 1.16 (95% CI 0.77–1.74, P=0.49): planning a section did not protect the babies, and it meant a major abdominal operation in 9 out of 10 cases. RCOG grades the matching monochorionic diamniotic statement A: vaginal birth is the appropriate goal unless cesarean is indicated.

Two realities before labor: RCOG recorded presentation order changing before delivery in 5.9% of vaginal and 20.3% of cesarean deliveries, and the second twin usually arrives within minutes under continuous monitoring, sometimes needing repositioning or emergency section.

What the third trimester actually looks like

Expect a heavier, shorter, more monitored third trimester than a singleton: the difference is logistics as much as risk.

Practical adjustments:

• Plan time off work before 37 weeks, with two car seats and a stroller ready by 30 weeks.
• Iron and folate reviewed at the anomaly scan; twins deplete iron faster.
• A named fetal medicine contact, so changed measurements or breathlessness get triaged.
• A written birth plan: week, mode, and what happens if the second twin does not turn.

Worth asking your clinic: how chorionicity was recorded and whether that happened before 14 weeks, who reads the fluid values and at what threshold you are called in, whether the unit performs fetoscopic laser, and your planned birth week.

Three IVF twin pregnancies, managed three different ways

Anonymized composite illustrations drawn from common clinical scenarios: names, amounts and details are altered and identify no real person.

Case 1 — age 34, Los Angeles, two embryos, Di-Di, delivered 38+3

Dana, 34, transferred two blastocysts in a single IVF cycle costing $23,800. The 12-week scan showed two placentas, a lambda sign and two sexes: dichorionic diamniotic.

Growth scans at 20, 24, 28, 32 and 36 weeks were normal. Birth was planned at 38+1, and after spontaneous labor she delivered both boys vaginally at 38+3, weighing 2.9 kg and 2.7 kg; delivery charges came to $14,200 and neither baby needed the NICU.

“I was the lucky kind of twin pregnancy, they kept saying. I only understood when my friend with a shared placenta was scanned every two weeks for five months,” she said.

Difficulty: insurance covered anesthesia only for cesarean, so her epidural in labor needed a written indication letter at 36 weeks.

Case 2 — age 31, Shanghai, one frozen blastocyst, Mo-Di, delivered 36+0

Wei, 31, transferred a single thawed day-5 blastocyst in a cycle costing ¥118,000 including medication and genetic testing. At 7 weeks the scan showed one sac and two heartbeats: monochorionic diamniotic.

Two-weekly surveillance began at 16 weeks. At 22 weeks her deepest vertical pockets were 1.8 cm and 9.4 cm: fluid discordance short of the 10 cm polyhydramnios line, so not yet stage I TTTS, with a fetal medicine referral. Values held on the same side of the line for eight weeks, so the team monitored rather than operated. Steroids at 34 weeks, then a cesarean at 36+0; both girls weighed 2.4 kg and 2.1 kg, the smaller spending 9 days in a special-care cot for feeding. Total cost including the extra monitoring and admission: about ¥215,000.

“One embryo, two babies, and a placenta to share. Nobody in my family understood why I was scanned more than the woman who transferred two,” she recalled.

Difficulty: her employer counted maternity leave from the delivery date, so 14 weeks of scan visits came out of personal leave.

Case 3 — age 33, Bangkok, one embryo, Mo-Mo, delivered 32+3

Priya, 33, had one blastocyst transferred at a Bangkok clinic for $16,500. The 11-week scan could not find a dividing membrane: monochorionic monoamniotic.

Cord entanglement was visible on Doppler from 18 weeks. Admitted at 28 weeks for continuous monitoring, she delivered by cesarean at 32+3. Both boys were alive and well but required ventilation, 21 days and 34 days in the NICU, and the neonatal bill reached $184,000, which her insurer covered only after an appeal.

“We were told the word ‘monoamniotic’ and then given a date two months early. There was no negotiation in it,” she said.

Difficulty: cross-border discharge paperwork plus a policy exclusion for neonatal intensive care abroad became a two-month claim dispute.

FAQ

Q: How many weeks are IVF twins usually carried?

Monochorionic diamniotic twins are offered birth from 36+0 weeks, dichorionic twins from 37, and monoamniotic twins by cesarean at 32+0–34+0 weeks.

Q: Does it matter that I transferred two embryos and only one implanted?

Not usually: one implanted embryo gives one singleton, though it can still split, and 1 sac with 2 heartbeats is a monochorionic pregnancy. Surveillance follows the scan, not the transfer record.

Q: Can my twins be monochorionic if I transferred two embryos?

Uncommon but possible: both embryos implant and 1 stops developing early, or 1 splits. Since 70% of monozygotic pairs are monochorionic, have chorionicity recorded on the scan report.

Q: How often will I be scanned if my twins share a placenta?

Every 2 weeks from 16+0 weeks until birth under RCOG’s guideline, recording fluid, umbilical artery Doppler and both bladders.

Q: What is the chance of twin-to-twin transfusion syndrome?

Up to 15% of monochorionic pregnancies, per RCOG, and none in dichorionic twins. After laser treatment, TTTS recurs in up to 14%.

Q: Are IVF twins more likely to be premature than naturally conceived twins?

Yes: in the meta-analysis of 802,462 twin pregnancies, ART-conceived twins had 1.26 times the odds of birth before 37 weeks and 1.33 times before 34 weeks.

Q: Can I have a vaginal birth with twins?

Yes: with the leading twin head-down at 32+0–38+6 weeks, planned vaginal birth is evidence-supported — in the 2,804-woman Twin Birth Study adverse perinatal outcome was 2.2% (planned cesarean) vs 1.9% (planned vaginal), odds ratio 1.16 (95% CI 0.77–1.74).

Q: When is chorionicity hardest to determine?

After about 14 weeks, when placentas fuse and the dividing membrane thins, which is why RCOG records it at the 11+0–13+6 week scan.

Planning the rest of your twin pregnancy

Ask for your chorionicity in writing, get it recorded before 14 weeks, and treat the two-weekly monochorionic calendar as non-negotiable: it turns TTTS from a surprise into a scheduled finding.

Choose a clinic on its obstetric capability, not only its laboratory: compare centers in our hospital directory and check for a named fetal medicine unit. The IVF cost guide breaks down costs, including NICU exposure.

This information is educational and does not replace medical advice. Twin pregnancies are managed individually and delivery timing can change; ask your own obstetric or fetal medicine team about your scans.

How this guide was written

The ProIVF Medical Editorial Team drafted this guide from RCOG Green-top Guideline No. 51, SMFM checklists and consult series, ACOG’s multifetal gestation bulletin, and PubMed-indexed cohorts and trials; the ProIVF Medical Advisory Board reviewed clinical interpretation.

ProIVF is an independent information platform: we do not provide treatment, we do not receive commissions from any clinic linked here, and clinic partnerships do not influence our editorial decisions. See our editorial standards.

Last updated: 8 October 2026

References

1. Royal College of Obstetricians and Gynaecologists. Management of Monochorionic Twin Pregnancy. Green-top Guideline No. 51. 2017.
2. Society for Maternal-Fetal Medicine. Consult Series #72: Twin-twin transfusion syndrome and twin anemia-polycythemia sequence.
3. American College of Obstetricians and Gynecologists. Multifetal Gestations: Twin, Triplet, and Higher-Order Multifetal Pregnancies. Practice Bulletin, 2021.
4. Barrett JF, et al. A randomized trial of planned cesarean or vaginal delivery for twin pregnancy. N Engl J Med. 2013. PMID 24088091.
5. Marleen S, et al. Maternal and perinatal outcomes in twin pregnancies following assisted reproduction: a systematic review and meta-analysis involving 802,462 pregnancies. Hum Reprod Update. 2024. PMID 38345641.
6. Lee HJ, et al. Gestational age at delivery and neonatal outcome in uncomplicated twin pregnancies. Obstet Gynecol Sci. 2016. PMID 26866030.