Table 5. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy of ultrasound in the first, second and third trimesters of pregnancy.

Trimester	Sensitivity	Specificity	PPV	NPV	Accuracy	+ LH	- LH
First	14.06%	98.65%	39.13%	94.90%	93.73%	10.0	0.87
Second	27.78%	98.14%	45.45%	96.06%	94.43%	14.6	0.73
Third	23.91%	97.76%	36.67%	95.94%	93.95%	10.9	0.78

PPV = positive predictive value; NPV = negative predictive value; +LH = positive likelihood ratio; -LH = negative likelihood ratio.