If you're asking when clubfoot develops in pregnancy, the answer is that the structural changes begin early — during the first trimester — though the condition may not become detectable on ultrasound until much later. Understanding the timeline of fetal foot development helps parents make sense of their child's diagnosis and prepares them for what comes next. This trimester-by-trimester guide covers how the foot forms, when clubfoot originates, and when it can be identified.
How the Fetal Foot Develops: A Timeline
To understand when clubfoot develops, it helps to know how a normal foot forms during pregnancy.
Weeks 4-8: Limb Bud Formation
The lower limb buds appear at approximately 4 weeks of gestation and undergo rapid differentiation through week 8. By 6 weeks, the basic template of the foot is established, with five distinct toe rays visible. The bones of the foot are initially cartilaginous — they will not begin to ossify (harden into bone) until later in pregnancy.
During this critical window, the genes responsible for limb patterning — including those in the PITX1, TBX4, and HOX gene families — direct the development of bones, muscles, tendons, and ligaments in the foot. Disruption to any of these developmental pathways can contribute to the formation of clubfoot. This is the period when the structural basis of clubfoot is established, even though the deformity is far too small to detect at this stage.
Weeks 8-12: Foot Rotation and Positioning
Between 8 and 12 weeks of gestation, the fetal foot undergoes a natural rotation. All fetuses start with their feet pointing inward (a position similar to clubfoot), and during this period, the feet gradually rotate to face forward and downward. In clubfoot, this rotation fails to complete normally, leaving the foot in its inverted, adducted, and equinus position.
By the end of the first trimester, the underlying clubfoot deformity is present, though the fetus is still only about 6 centimetres long and the foot itself is tiny. Current imaging technology cannot reliably detect clubfoot at this stage.
Weeks 12-20: Growth and Ossification
During the second trimester, the foot grows significantly and the bones begin to ossify. The talus, calcaneus, and other tarsal bones take shape in their displaced positions. The soft tissues — muscles, tendons, and ligaments — develop around the abnormal skeletal framework, creating the tissue tightness and imbalance that characterise clubfoot.
It is during this period that clubfoot first becomes potentially visible on ultrasound, typically from around 16-18 weeks, though reliable detection is more common from 20 weeks onward.
Weeks 20-40: Continued Development
Through the second and third trimesters, the clubfoot deformity becomes more established. The foot continues to grow in its abnormal position. However, because the bones remain partly cartilaginous until well after birth, the deformity retains some plasticity — this is precisely why the Ponseti method, which gently repositions the foot through serial casting in infancy, is so effective.
When Can Clubfoot Be Detected on Ultrasound?
The 20-Week Anomaly Scan
In the UK, all pregnant women are offered a detailed ultrasound scan at 18-21 weeks of gestation (commonly called the 20-week scan or anomaly scan). This is the standard point at which clubfoot is most often identified prenatally.
During this scan, the sonographer examines the fetal anatomy systematically, including the limbs and feet. Clubfoot can be identified when the foot is seen in a fixed equinovarus position — turned inward and pointing downward — that does not change with fetal movement. The sonographer looks at the sole of the foot in relation to the lower leg; in a normal foot, the sole faces downward, whereas in clubfoot, it faces inward or upward.
For detailed information about what happens after a prenatal diagnosis, see our prenatal clubfoot diagnosis guide.
Detection Rates and Limitations
Prenatal detection of clubfoot varies significantly between centres. Studies report detection rates ranging from 30% to 80%, depending on:
- Sonographer experience: Skilled operators at specialist centres detect clubfoot more reliably than general screening clinics
- Fetal position: If the baby's feet are tucked away or obscured by other body parts, assessment may be difficult
- Severity: Severe clubfoot is more readily identified than mild cases
- Bilateral vs unilateral: Bilateral clubfoot (both feet affected) tends to be detected more reliably than unilateral
- Gestational age: Later scans (after 24 weeks) are more reliable for detecting clubfoot than scans at 18-20 weeks
Because prenatal detection is not 100% reliable, many cases of clubfoot are first identified at the newborn examination after birth. This is normal and does not indicate a failure of antenatal care.
Earlier Detection: Is It Possible?
Some research has explored whether clubfoot can be detected earlier than 20 weeks. First-trimester scans (11-14 weeks) can occasionally show foot abnormalities, but at this early stage, the feet are so small that false-positive and false-negative rates are high. Currently, early pregnancy scans are not considered reliable for clubfoot detection, and a normal 12-week scan does not exclude the condition.
Advanced 3D and 4D ultrasound can provide clearer images of fetal feet, but these are not routinely used in NHS screening. They may be offered at specialist fetal medicine centres when a standard 2D scan raises concerns.
What Causes Clubfoot to Develop During Pregnancy?
The formation of clubfoot is now understood to result from a combination of genetic susceptibility and environmental factors that interact during the critical first-trimester developmental window.
Genetic Factors
Research has identified several gene variants associated with clubfoot, particularly in genes involved in limb patterning (PITX1), muscle development (TPM1, TPM2), and connective tissue formation. Having a first-degree relative with clubfoot increases a child's risk by approximately 20-30 times compared to the general population. For a full discussion, see our article on clubfoot genetics and heredity.
Environmental Risk Factors
Several environmental factors during early pregnancy have been linked to increased clubfoot risk:
- Maternal smoking: The most consistently identified environmental risk factor. Smoking during the first trimester increases clubfoot risk by approximately 20-30%.
- Selective serotonin reuptake inhibitors (SSRIs): Some studies suggest a small increase in clubfoot risk with SSRI antidepressant use in early pregnancy, though the absolute risk remains very low and the benefits of treating maternal depression typically outweigh this risk.
- Low amniotic fluid (oligohydramnios): Reduced fluid around the fetus can restrict limb movement and contribute to positional deformities, though this is a more significant factor for positional talipes than for structural clubfoot.
- Folic acid deficiency: Inadequate folic acid intake in early pregnancy has been associated with higher clubfoot rates in some population studies.
For a comprehensive overview, see our guide on what causes clubfoot.
What Happens After a Prenatal Diagnosis
If clubfoot is identified on the 20-week scan, the typical NHS pathway is:
- Detailed ultrasound: A fetal medicine specialist reviews the scan to confirm the diagnosis and check for any associated conditions
- Genetic counselling: Offered to discuss whether further testing (such as amniocentesis) is warranted. Isolated clubfoot rarely requires invasive testing, but if other anomalies are suspected, karyotyping may be recommended to check for chromosomal conditions
- Referral to paediatric orthopaedics: Some hospitals arrange a prenatal meeting with the orthopaedic team so parents can learn about the Ponseti method and treatment plan before birth
- Birth plan: Clubfoot does not affect the mode of delivery. Vaginal birth is perfectly safe, and no special delivery arrangements are needed
- Postnatal assessment: After birth, the baby is examined by the orthopaedic team and Ponseti casting typically begins within 1-2 weeks
Can Clubfoot Be Prevented During Pregnancy?
Because the genetic component of clubfoot is not modifiable, complete prevention is not currently possible. However, the following measures may reduce risk:
- Take folic acid: 400 micrograms daily from before conception until 12 weeks of pregnancy (NHS recommendation)
- Avoid smoking: Quitting before or early in pregnancy reduces clubfoot risk along with many other health benefits
- Discuss medications: If you take SSRIs or other medications, talk to your GP or obstetrician about the risk-benefit balance — do not stop medication without medical advice
- Maintain a balanced diet: Adequate nutrition supports normal fetal development broadly
Even with all recommended precautions, clubfoot can still occur. Parents should not blame themselves for their child's diagnosis — it is not caused by anything they did or failed to do during pregnancy.
Frequently Asked Questions
Q: Can stress during pregnancy cause clubfoot?
A: There is no reliable scientific evidence linking maternal stress to clubfoot. While extreme stress can affect pregnancy outcomes in general terms, it has not been identified as a specific risk factor for clubfoot development. Parents should not feel that their emotional state during pregnancy contributed to their child's condition.
Q: If clubfoot wasn't seen on the 20-week scan, can it develop later?
A: Clubfoot is present from the first trimester, but it is not always detected on the 20-week scan. If the scan was normal, the most likely explanation is that the foot position made detection difficult, not that the condition developed later. Occasionally, very mild clubfoot may not be apparent until birth, when it is picked up at the newborn examination.
Q: Does the position of the baby in the womb cause clubfoot?
A: Fetal position can cause positional talipes (a milder, flexible foot deformity) but does not cause true structural clubfoot. Positional talipes typically resolves without treatment within weeks of birth. True clubfoot involves structural changes to the bones, muscles, and tendons that are established during the first trimester and require treatment with the Ponseti method.
Q: Is clubfoot more common in boys or girls?
A: Yes, clubfoot is approximately twice as common in boys as in girls. The reasons for this sex difference are not fully understood but may relate to differences in limb development timing and hormonal influences during pregnancy. Both boys and girls respond equally well to Ponseti treatment.
Q: Can I have a natural birth if my baby has clubfoot?
A: Absolutely. Clubfoot does not affect the birth process in any way. Vaginal delivery is safe and no caesarean section is needed on account of clubfoot alone. The condition is managed after birth through postnatal assessment and Ponseti casting, typically starting within the first two weeks of life.