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Fetal Biometry

Cervical Length (CL): Prematurity Risk

see Fetal Medicine Foundation (
)
Cervical Length Risk
The following tables give the percentage chance of delivery before a given gestational age, and are based on a transvaginally measured cervical length measured at 20-26 weeks, using the FMF Cervical Length Risk .
A reported significantly short cervix at an early gestation should, ideally, be confirmed by a level III scanning unit. Whether funnel width and/or funnel length improves predictability is not proven. If the cervical length changes dynamically, then the shortest length should be used.
image.png
From 14-30 weeks the 10th centile is 25mm, the median 35-40mm, and the 90th centile 50mm. If the cervix measures >35mm at 18-22 weeks, the chance of delivery is <4% even for high risk patients.
The higher the baseline risk (previous pregnancy outcome), the shorter the cervix, and the earlier the shortened cervix is measured; the higher the PPV of preterm delivery. Even for patients destined to have a significantly preterm delivery, the odds of the cervix being short at a 10-14 weeks scan is very low.
The role of best rest, progesterone, antibiotics, and cerclage remains difficult, with an absence of high quality randomised trials; care will be individualised with shared decision making.
ROD: Risk of Delivery
CL vs ROD <28w- Primip
0
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GA
10mm
15mm
20mm
25mm
30mm
1
<28w
6.6%
2.0%
0.7%
0.3%
0.1%
2
<31w
11%
4.2%
1.8%
0.8%
0.4%
3
<34w
18.4%
8.3%
4.1%
2.1%
1.1%
4
<37w
38.1%
18.8%
10.7%
6.7%
4.5%
There are no rows in this table
CL vs ROD <28w- Multip: Previous delivery >36w
0
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GA
10mm
15mm
20mm
25mm
30mm
1
<28w
3.6%
1.1%
0.4%
0.2%
0.1%
2
<31w
6.3%
2.4%
1.1%
0.5%
0.2%
3
<34w
11.1%
5.1%
2.5%
1.3%
0.7%
4
<37w
25.2%
12.6%
7.3%
4.6%
3.1%
There are no rows in this table
CL vs ROD <28w- Multip: Previous delivery 24-33w
1
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GA
10mm
15mm
20mm
25mm
30mm
1
<28w
12.3%
3.8%
1.4%
0.6%
0.3%
2
<31w
28.3%
11.7%
5.3%
2.5%
1.2%
3
<34w
58.0%
28.0%
14.3%
7.4%
3.9%
4
<37w
99.0%
50.6%
28.6%
17.4%
11.3%
There are no rows in this table

Chart of CL vs ROD<28w- Multip: Previous delivery 24-33w
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