Evaluating the Agreement of Risk Categorization for Fetal Down Syndrome Screening between Ultrasound-Based Gestational Age and Menstrual-Based Gestational Age by Maternal Serum Markers

Table 2

The number of different days between LMP-based GA and US-based GA in gestational age estimation.

Mean different days	First trimester		Second trimester		Total
	N	%	N	%	N	%
0	376	9.3	318	7.9	694	8.6
1–3	1837	45.3	1600	39.8	3437	42.6
4–7	1302	32.1	1194	29.7	2496	30.9
8–14	451	11.1	615	15.3	1066	13.2
15–21	50	1.2	163	4.1	213	2.6
22–28	18	0.4	70	1.7	88	1.1
>28	21	0.5	56	1.4	77	1.0
Total	4055	100.0	4016	100.0	8071	100.0