First Trimester Cervical Funneling: Rare Case Highlighted by Transvaginal Ultrasound
Cervical funneling occurs when the internal os of the cervix opens prematurely, forming a funnel shape while the external os remains closed and functional. In pregnant women, the average cervical length measures 3.5–4 cm between 14 and 30 weeks. A transvaginal cervical length under 2.5 cm between 14 and 24 weeks signals an abnormal finding, and shorter cervices increase the risk of preterm birth.
Data on first trimester cervical length remain limited because early measurements are less accurate, and no interventions are currently recommended at this stage. Additionally, first-trimester imaging can make it difficult to distinguish the cervix from the lower uterine segment.
Transvaginal ultrasound remains the gold standard for cervical length screening. Clinicians should ensure the patient’s bladder is empty to avoid compressing the cervix or masking any funneling. In this case study, we present a rare first trimester cervical funneling finding, highlighting the importance of early detection for understanding preterm birth risk.
Case Study
This 35-year-old, G3P1, patient presented to the ED on 7.2 with vaginal bleeding. LMP was 5.20. The patient has had one prior SAB and one previous cesarean delivery. Below, you can see the sagittal view of the uterus and cervix in the axial plane or neutral position.
Notice that the patient’s bladder is not completely empty in the image on the left. In the image on the right, a 6w3d gestational sac is noted with no fetal pole or yolk sac seen. Because of this, a quant was also drawn, which was 48.089.
Here, the cervix appears normal. No evidence of funneling. There is normal cervical mucus and a Nabothian cyst seen.
The patient was discharged and followed up with our office on 7.18. The in-office ultrasound revealed the following:
A uterus in the axial plane or neutral position again and funneling in the cervix.
A large amount of blood or clot is also seen within the funnel. There is a viable IUP measuring 8w2d with a FHR of 177bpm as pictured below.
Because the cervix is very dynamic and can change quickly in a short amount of time, I usually look away from cervix several times before returing to take official measurements. I used this time to evaluate the ovaries and adnexa, as we should in each first trimester scan.
I then returned to the cervix and obtained cervical length measurements.
The functional or closed part of the cervix measured 1.41cm. The funnel was 3.31cm in length and 2.2cm in width. It is important to remember that it is difficult to see where the LUS ends and where the cervix begins in the first trimester, so these measurements could be a little long.
The patient was referred to MFM, but the referral was rejected as they assumed the patient would miscarry and there is no intervention that can be done in the first trimester. I should add that the patient also reports no further bleeding since her visit to the ED.
The patient returned one month later on 8.16. Again, still no further bleeding. Only a small amount of dark discharge.
There is a viable 12w3d IUP as seen below:
The cervix is funneling, and the closed part of the cervix is now measuring 1.26cm.
Again, a large amount of blood/clot is seen in the funnel.
Another referral to MFM was placed and they are seeing the patient on 9.13 @ 16 weeks. In the meantime, the patient is following up with us again at 14+ weeks to re-evaluate the cervix.
At the follow up exam, the patient still has a viable pregnancy. FHR is 154 as pictured below. Biometric measurements are also on track.
The cervix is still funneled with approximately 1.5cm of closed, functional cervix on this exam. Blood/clot is still seen within the funnel. Membranes are seen lying across the internal os.
The patient is still scheduled to follow up with our MFM department around 16 weeks and will likely be headed for a cerclage at the earliest available time. To learn more and dive deeper, register for one of our monthly workshops , or a custom training to suit your needs.