Validation of second trimester miscarriages and spontaneous deliveries

Figures & data

Figure 1 Flowchart of selection for validation.

Table 1 Distribution and validity of the diagnoses of miscarriage and spontaneous preterm delivery in the second trimester in the Danish National Patient Registry and the Danish Medical Birth Registry

Registry	Sample, n	Available records, n (%)	Category	Confirmed diagnoses, n	Positive predictive value % (95% CI)
Danish National Patient Registry	408	369 (90.4)	Spontaneous onset	335	90.8 (87.9–93.8)
			Gestational age ±1 week	259	70.2 (65.5–74.9)
			Gestational age ±2 weeks	360	97.6 (96.0–99.2)
			Miscarriage weeks 16–27	330	89.4 (86.3–92.5)
Danish Medical Birth Registry	332	313 (94.2)	Spontaneous onset	298	95.2 (92.8–97.6)
			Gestational age ±1 week	280	89.5 (84.6–92.8)
			Gestational age ±2 weeks	306	97.7 (96.0–99.4)
			Spontaneous delivery weeks 16–27	291	92.9 (90.1–95.8)
Total	740	682 (92.3)	Miscarriage/spontaneous delivery weeks 16–27	621	91.1 (88.6–93.0)

Abbreviation: CI, confidence interval.

Table 2 Frequencies of risk factors and pregnancy complications in the first spontaneous second trimester delivery/miscarriage

	National Patient Registry (n=682)	P-value	Medical records (n=682)	Medical Birth Registrya (n=313)	P-value
Uterine congenital anomaly	23 (3.4)	0.29	31 (4.5)	–
Uterine fibroids	22 (3.2)	0.48	27 (4.0)	–
Thrombophilia	15 (2.2)	0.73	17 (2.5)	–
Cervical conization	50 (7.3)	0.46	58 (8.5)	–
Cervical insufficiency	198 (29.0)	0.02	149 (21.8)	–
Antepartum fetal death	10 (1.5)	<0.001	41 (6.0)	–
Multiple pregnancies	63 (9.2)	0.002	106 (15.5)	30 (9.5)	0.003
Major fetal anomaly	5 (0.7)	0.04	14 (2.1)	6 (1.9)	0.89
Placental insufficiency/intrauterine growth retardation	16 (2.3)	0.10	27 (4.0)	–
Placental abruption	25 (3.7)	0.05	41 (6.0)	24 (7.6)	0.36
Antepartum vaginal bleeding	36 (5.3)	<0.001	119 (17.4)
Preterm premature rupture of membranes	82 (12.0)	<0.001	169 (24.7)	61 (19.5)	0.14

Note:

a Incidences are based on deliveries recorded in The Danish Medical Birth Registry.

Table 3 Sensitivity, specificity, positive predictive value, and kappa scores of pregnancy complications recorded in the Danish National Patient Registry and the Danish Medical Birth Registry

Pregnancy complication	Danish National Patient Registry				Danish Medical Birth Registry
	Sensitivity, % (95% CI)	Specificity, % (95% CI)	Positive predictive value, % (95% CI)	Kappa (95% CI)	Sensitivity, % (95% CI)	Specificity, % (95% CI)	Positive predictive value, % (95% CI)	Kappa (95% CI)
Antepartum fetal death
Miscarriages	22.7 (12.0–38.2)	100 (98.5–100)	100 (65.6–100)	0.34 (0.18–0.50)	–	–	–	–
Deliveries	–	–	–	–	–	–	–	–
Multiple pregnancies
Miscarriages	40.9 (30.0–53.7)	99.3 (97.6–99.9)	93.1 (77.2–99.2)	0.52 (0.39–0.64)	–	–	–	–
Deliveries	78.0 (62.0–88.9)	99.3 (97.2–99.9)	94.1 (78.9–99.0)	0.83 (0.74–0.93)	82.4 (65.7–93.2)	99.3 (97.4–99.8)	93.3 (77.9–99.2)	0.86 (0.77–0.96)
Major fetal anomaly
Miscarriages	27.2 (7.3–60.9)	100 (98.7–100)	100 (30.9–100)	0.42 (0.10–0.75)	–	–	–	–
Deliveries	70.0 (35.4–91.9)	100 (98.4–100)	100 (56.1–100)	0.82 (0.62–1.00)	60.0 (27.4–86.3)	100 (98.4–100)	100 (51.9–100)	0.74 (0.50–0.99)
Placental insufficiency/intrauterine growth retardation
Miscarriages	50.0 (17.4–82.6)	100 (98.7–100)	100 (39.6–100)	0.66 (0.35–0.97)	–	–	–	–
Deliveries	52.6 (29.5–74.8)	99.3 (97.3–99.9)	83.3 (50.9–97.1)	0.63 (0.43–0.83)	–	–	–	–
Placental abruption
Miscarriages	14.2 (0.7–58.0)	100 (98.7–100)	1 (5.4–100)	0.25 (–0.15–0.64)	–	–	–	–
Deliveries	65.7 (47.7–80.3)	99.6 (97.6–100)	95.8 (76.9–99.8)	0.76 (0.63–0.88)	62.9 (44.9–78.0)	99.6 (97.7–100)	95.6 (92.2–97.5)	0.74 (0.60–0.87)
Preterm premature rupture of membranes
Miscarriages	22.8 (15.0–33.0)	99.6 (97.7–100)	95.5 (75.1–99.8)	0.30 (0.20–0.41)	–	–	–	–
Deliveries	68.8 (57.1–78.6)	97.0 (93.7–98.7)	88.3 (76.8–94.8)	0.71 (0.62–0.81)	71.4 (59.8–80.9)	97.9 (94.8–99.2)	91.7 (80.9–96.9)	0.75 (0.66–0.84)
Cervical insufficiency
Miscarriages	76.3 (64.5–85.4)	86.9 (82.0–90.3)	58.5 (47.9–68.0)	0.57 (0.47–0.67)	–	–	–	–
Deliveries	77.9 (66.5–86.4)	81.4 (75.7–86.0)	57.7 (47.6–67.1)	0.55 (0.45–0.65)	–	–	–	–

Abbreviation: CI, confidence interval.

Table 4 Sensitivity, specificity, positive predictive value, and kappa scores of risk factors of spontaneous second trimester delivery/miscarriage

Risk factor	Sensitivity, % (95% CI)	Specificity, % (95% CI)	Positive predictive value, % (95% CI)	Kappa (95% CI)
Uterine congenital anomaly	71.5 (51.7–85.2)	99.8 (98.9–100)	95.0 (95.0–98.0)	0.81 (0.69–0.92)
Uterine fibroids	74.1 (53.7–88.9)	99.7 (98.9–100)	90.9 (70.8–99.6)	0.81 (0.69–0.93)
Thrombophilia	88.2 (63.6–98.5)	100 (99.5–100)	100 (78.2–100)	0.94 (0.85–1.00)
Cervical conization	84.5 (72.6–92.7)	99.8 (99.1–100)	98.0 (89.4–99.9)	0.90 (0.84–0.96)

Abbreviation: CI, confidence interval.

Table 5 Sensitivity, specificity, positive predictive value, and kappa scores of different types of cervical cerclage

	Sensitivity, % (95% CI)	Specificity, % (95% CI)	Positive predictive value, % (95% CI)	Kappa (95% CI)
Elective vaginal cerclage	82.7 (73.8–89.2)	99.5 (98.4–99.9)	96.6 (89.8–99.1)	0.87 (0.82–0.93)
Urgent cerclage	90.3 (75.9–96.8)	98.2 (96.8–99.1)	77.1 (62.3–87.5)	0.82 (0.73–0.91)
All vaginal cerclages	92.2 (86.1–95.8)	100 (99.1–100)	100 (96.4–100)	0.95 (0.92–0.98)
Abdominal cerclage	85.7 (66.4–95.3)	100 (99.3–100)	100 (82.5–100)	0.92 (0.84–1.00)

Abbreviation: CI, confidence interval.

Table S1 Definitions and codes of risk factors, pregnancy complications, and cerclage

	Definition	Codes
Fetal anomaly	Lethal or major fetal anomalies classified by complexity classification system:^Citation30 anencephalus, microcephalus, encephalocele, esophageal atresia, bilateral multicystic renal disease, renal agenesia, omphalocele, pentagology of Cantrell, Pierre Robin sequence, trisomy 9,13,18, and 21,22q11 syndrome, 45×0 high and lethal complex cardiac malformations: truncus arteriosus communis, complete transposition of the great arteries, Isomeric auricularum atriorum, tetralogy of Fallot, hypoplastic left heart, dextrocardia, levocardia, congenital heart block, acardia	DO350–DO351, DQ00, DQ01, DQ02, DQ04, DQ390, DQ60–DQ61, DQ792, DQ85–DQ87, and DQ90–DQ900
Multiple pregnancies	≥2 fetuses	DO30–DO309, DO31, and DO84
Antepartum fetal death Placental abruption	Intrauterine fetal death before the onset of labor	DO021
	Premature separation of the placenta from the uterine wall that is diagnosed by	DO45 and
	1. Ultrasonic retroplacental hematoma	DO450–DO459
	2. Macroscopic hematoma
	3. Histological evidence of abruption
Placental insufficiency/intrauterine growth retardation	Histological evidence of vasculitis/infarction/necrosis/other stated in the placental pathology report or impaired fetal growth stated in the medical record	DO438–DO438E and DO365
Cervical insufficiency	Painless cervical shortening and/or dilation in singleton pregnancies after exclusion of major fetal anomalies, placental abruption, and other causes of spontaneous second trimester delivery	DO343, DO343A, DO343B, and DZ875A
Preterm premature rupture of membranes	Rupture of the amniotic membranes before the onset of labor	DO42–DO429
Antepartum vaginal bleeding	Extensive fresh vaginal bleeding without regular contractions, with or without PPROM	DO46–DO469
Thrombophilia	Abnormality of blood coagulation that increases the risk of thrombosis	DD685, DD685A–DD685M, DD686D, and DD686E
	1. Inherited: factor V Leiden and protrombin mutations and antithrombin III, protein S, and protein C deficiencies
	2. Acquired: antiphospholipid syndrome
Congenital uterine anomaly	Uterine agenesis, uterus didelphys, bi- and unicornuate uerus and arcuate, subseptate, and septate uterus	DQ51–DQ519
Uterine fibroid	Submucosal or intramurale uterine fibroids	DD250–DD251
Cervical conization	Excision of a conus of the cervix by cold knife or loop excision before the first second trimester delivery	KLDC00–13, KLDC20–23, and KLDC96a
Vaginal cerclage	The vaginal placement of cervical stitches on the pregnant uterus either electively in patients with a history of cervical insufficiency or urgent/emergency cerclage patients with short or dilated cervix	KMAB00a
Abdominal cerclage	Surgical procedure in which a band is placed on the cervico-isthmic junction via laparoscopy or laparoscopy	KLDD10, KLDD10A, and KLDD10Ba

Note:

a Danish codes for surgical procedures.

Abbreviation: PPROM, preterm premature rupture of membranes.

Table S2 Diagnoses recorded in The Danish National Patient Registry (DNPR) by the presence of the condition in medical records

Diagnosis recorded in DNPR	Presence of condition in medical records
	Yes	No	Total
Multiple pregnancies, miscarriages (030)
Yes	27	2	29
No	38	302	340
Total	65	304	369
Multiple gestations, deliveries (030)
Yes	7	0	7
No	34	272	306
Total	41	272	313
Major fetal anomaly, miscarriages
Yes	2	0	32
No	6	361	367
Total	8	361	369
Major fetal anomaly, deliveries
Yes	1	2	3
No	8	302	310
Total	9	304	313
Placental insufficiency/intrauterine growth retardation miscarriages (O438/O365)
Yes	4	0	4
No	4	361	365
Total	8	361	369
Placental insufficiency/intrauterine growth retardation, deliveries (O438/O365)
Yes	10	2	12
No	9	292	301
Total	19	294	313
Placental abruption, miscarriages (O45)
Yes	1	0	1
No	5	363	368
Total	6	363	369
Placental abruption, deliveries (O45)
Yes	23	1	24
No	12	277	289
Total	35	278	313
Antepartum fetal deaths, miscarriages (O021)
Yes	10	0	10
No	34	325	359
Total	44	325	369
Antepartum bleeding, miscarriages (O46)
Yes	7	0	7
No	64	298	362
Total	81	298	369
Antepartum bleeding, deliveries (O46)
Yes	28	1	29
No	20	264	284
Total	48	265	313
Preterm premature rupture of membranes, miscarriages (O42)
Yes	21	1	22
No	71	276	347
Total	92	277	369
Preterm premature rupture of membranes, deliveries (O42)
Yes	53	7	54
No	24	229	259
Total	77	236	313
Cervical insufficiency, miscarriages (Z875A, O343, and O343A/B)
Yes	55	39	94
No	17	258	275
Total	72	297	369
Cervical insufficiency deliveries (Z875A, O343, and O343A/B)
Yes	60	44	104
No	17	192	209
Total	77	236	313

Table S3 Diagnoses recorded in The Danish Medical Birth Registry (DMBR) by the presence of the condition in medical records

Diagnosis recorded in DMBR	Presence of condition in medical records
	Yes	No	Total
Multiple pregnancies (030)
Yes	28	2	30
No	6	277	283
Total	34	279	313
Major fetal anomaly
Yes	6	0	6
No	3	304	307
Total	9	304	313
Placental abruption (O45)
Yes	22	1	23
No	13	277	290
Total	35	278	313
Preterm premature rupture of membranes (O42)
Yes	55	5	60
No	22	231	253
Total	77	236	313

Table S4 Diagnoses recorded in the Danish National Patient Registry (DNPR) by the presence of the risk factor/surgical intervention observed in medical records

Diagnosis recorded in DNPR	Presence of risk factor in medical records
	Yes	No	Total
Congenital uterine anomaly (Q510–Q519)
Yes	22	1	23
No	9	650	659
Total	31	651	682
Uterine fibroids (D25–D259)
Yes	20	2	22
No	7	653	660
Total	27	655	682
Thrombophilia (D680–D682 and D685–D686)
Yes	15	0	15
No	2	665	667
Total	17	665	682
Cervical conization (KLDC)
Yes	49	1	50
No	9	623	632
Total	58	624	682

Table S5 Diagnoses recorded in The Danish National Patient Registry (DNPR) by the presence of the procedure in medical records

Diagnosis recorded in DNPR	Presence of procedure in medical records
	Yes	No	Total
Elective vaginal cerclage (KMAB00)
Yes	86	3	89
No	18	596	593
Total	102	599	682
Urgent/emergent cerclage (KMAB00)
Yes	37	11	48
No	4	630	634
Total	41	642	682
All vaginal cerclages (KMAB00)
Yes	130	0	130
No	11	541	552
Total	141	541	682
Abdominal cerclage (KLDD10)
Yes	24	0	24
No	4	354	358
Total	28	354	382

NellSWijngaardeCAPistoriusLRFetal Diag Ther2013334235240

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