MRI Fetal — body and placenta
Fetal thorax, abdomen and pelvis in three planes relative to the fetus, plus the placenta, the uterine wall and the maternal bladder interface where abnormal placentation is the question.
Typical, not policy
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Congenital diaphragmatic hernia, for lung volume assessment and liver position.
- Congenital lung malformation and airway obstruction, including planning for delivery-room intervention.
- Complex abdominal or genitourinary malformation where ultrasound is limited by oligohydramnios or maternal habitus.
- Suspected placenta accreta spectrum, particularly with an anterior placenta over a previous caesarean scar.
- Suspected fetal tumour, such as sacrococcygeal teratoma, requiring extent assessment.
Technique
- Single-shot fast spin-echo T2 in three fetal planes, with T1 for meconium, liver and haemorrhage.
- Diffusion-weighted imaging for renal and pulmonary tissue and for placental assessment.
- Balanced steady-state sequences for vascular structures and for rapid survey.
- For placental accreta assessment, sequences are angled to the uterine wall and bladder interface, and a moderately full maternal bladder helps define that interface.
Where it goes wrong
- Planes not referenced to the fetus, making volumetric measurement such as fetal lung volume unreliable.
- Ultrafast T2 alone for a placental question, omitting the T1 and diffusion sequences that contribute.
- Maternal bladder empty when the bladder-uterine interface is the structure being assessed.
- Fetal motion between planes making volumetry non-reproducible; repeated stacks are the accepted mitigation.
- Scanning at a gestation too early for the measurements the referrer intends to use.
Clinical questions that reach this study
Contrast
None
- No gadolinium. Placental assessment relies entirely on unenhanced T2, T1 and diffusion characteristics.
Acquisition
- Breathing
- Maternal free breathing with ultrafast sequences; breath-holding is used for some placental acquisitions where the mother can manage it.
- Preparation
- Supply the ultrasound report and the exact question; a fetal MRI without a stated ultrasound abnormality is rarely justifiable. Gestational age is essential — the study is generally most informative in the second half of pregnancy and small fetuses move more. Gadolinium is not given. Maternal sedation is not routine and should be a documented decision if considered. Position the mother for comfort; left lateral decubitus is often better tolerated in the third trimester than supine.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- MR safety screening for implants and foreign bodies· radiographer at scan
- Gadolinium in known or possible pregnancy· radiographer at scan