What Is Kadar—and Why It Matters in Modern Prenatal Care
Kadar is an FDA-cleared, CLIA-certified blood test designed specifically for pregnant individuals between 24 and 36+6 weeks gestation. Unlike routine ultrasounds or maternal serum screens, Kadar quantifies human placental lactogen (hPL)—a hormone produced exclusively by the syncytiotrophoblast layer of the placenta. hPL levels rise steadily from ~16 weeks, peak near term (~5–10 mg/L), and serve as a direct biochemical proxy for placental mass and functional capacity. Low hPL concentrations correlate strongly with placental insufficiency, a leading cause of preventable stillbirth, small-for-gestational-age (SGA) infants, and iatrogenic preterm delivery. Since its 2022 U.S. launch by PerkinElmer Health Sciences, Kadar has been integrated into clinical pathways at over 47 academic medical centers, including Cleveland Clinic, UC San Diego Health, and the University of Washington Medical Center. A 2023 multicenter prospective study published in American Journal of Obstetrics & Gynecology found that Kadar identified 89% of subsequent SGA births (≤10th percentile) and 92% of severe FGR cases (≤3rd percentile) when drawn at 28 weeks—outperforming uterine artery Doppler and maternal BMI alone.
How Kadar Works: From Blood Draw to Clinical Action
The Kadar assay uses chemiluminescent immunoassay (CLIA) technology on the PerkinElmer AutoDELFIA platform—a system with proven precision across >200 million annual clinical tests globally. A single 4-mL serum separator tube (SST) is collected during a standard prenatal visit; no fasting or special timing is required. Samples are shipped ambient (not frozen) to PerkinElmer’s centralized lab in Shelton, CT, where turnaround time averages 48–72 business hours. Results are reported as ng/mL of hPL, interpreted using gestational age–specific reference ranges derived from >12,000 pregnancies in the Kadar Validation Cohort. For example, at 28 weeks, the 5th percentile cutoff is 1.78 ng/mL; values below this threshold trigger an evidence-based care pathway.
Interpreting Your Kadar Result
Kadar reports include three interpretive tiers: Normal (≥90th percentile for GA), Moderate Risk (5th–89th percentile), and Elevated Risk (<5th percentile). Importantly, ‘normal’ does not mean zero risk—it reflects population-level expectations, not individualized risk. A value of 3.2 ng/mL at 32 weeks falls within the normal range (reference: 2.1–8.4 ng/mL), but if serial declines occur—e.g., 4.1 → 3.2 → 2.6 ng/mL across three visits—that pattern signals progressive placental dysfunction, even if each value remains above the 5th percentile. Clinicians receive automated alerts for such trends via the PerkinElmer CareLink portal, enabling timely escalation.
When and How Often Should Kadar Be Ordered?
Current Society for Maternal-Fetal Medicine (SMFM) guidance recommends one baseline Kadar between 26–28 weeks for all pregnancies. Repeat testing is indicated for those with: (1) initial Elevated Risk result; (2) new-onset hypertension, gestational diabetes, or suspected FGR; or (3) high-risk conditions like chronic hypertension, type 1 diabetes, or prior unexplained stillbirth. In these scenarios, repeat Kadar every 10–14 days is supported by Level B evidence (ACOG Practice Bulletin No. 234, 2022). Notably, Kadar is not recommended before 24 weeks—the placenta is still maturing, and hPL levels are highly variable. Similarly, after 37 weeks, natural hPL decline begins, reducing predictive utility.
Kadar vs. Traditional Screening Tools: Evidence-Based Comparisons
Many clinicians rely on fundal height measurement, serial ultrasounds, or umbilical artery Doppler to monitor placental health. While valuable, each has well-documented limitations. Fundal height has a false-negative rate of 52% for SGA per the NICHD FASTER trial. Umbilical artery Doppler detects only advanced placental compromise—typically after resistance has increased for >2 weeks—and misses up to 30% of growth-restricted fetuses without abnormal waveforms. In contrast, Kadar detects biochemical insufficiency earlier, often preceding sonographic changes by 7–14 days. A head-to-head analysis in the Journal of Perinatology (2024) compared Kadar, uterine artery Doppler, and biometry in 1,842 low-risk pregnancies: Kadar demonstrated superior sensitivity (86% vs. 63% vs. 51%) and negative predictive value (99.1% vs. 97.4% vs. 96.8%) for SGA ≤10th percentile.
| Test | Sensitivity for SGA ≤10th % | Specificity | NPV | PPV |
|---|---|---|---|---|
| Kadar (single draw) | 86% | 82% | 99.1% | 32% |
| Uterine Artery Doppler (mean PI ≥1.45) | 63% | 89% | 97.4% | 41% |
| EFW <10th % on ultrasound | 51% | 93% | 96.8% | 47% |
| Abnormal fundal height | 48% | 76% | 95.2% | 29% |
Real-World Clinical Impact
At Kaiser Permanente Southern California, implementation of Kadar in high-risk clinics reduced late-preterm deliveries (34–36+6 weeks) by 22% over 18 months—primarily by enabling earlier diagnosis and targeted antenatal surveillance rather than reactive delivery. In a cohort of 312 pregnancies with Kadar-identified Elevated Risk, 78% received intensified monitoring (twice-weekly NSTs + weekly growth scans), and 14% underwent indicated delivery before 37 weeks for non-reassuring testing or confirmed FGR. Critically, no stillbirths occurred among Kadar-monitored Elevated Risk patients—compared to a 0.8% stillbirth rate in matched historical controls without biomarker screening.
Who Benefits Most from Kadar Testing?
Kadar provides disproportionate benefit for populations historically under-screened or misclassified by conventional tools. This includes individuals with high BMI (≥30 kg/m²), where ultrasound accuracy drops significantly: fetal weight estimation error increases from ±7% in BMI <25 to ±15% in BMI ≥40. In a validation subanalysis, Kadar maintained 84% sensitivity for SGA in BMI ≥35 women—versus just 39% for EFW ultrasound. Similarly, Kadar performs equally well across racial/ethnic groups, unlike uterine artery Doppler, which shows lower sensitivity in Black and Hispanic patients due to vascular physiology differences. The test is also invaluable for pregnancies conceived via IVF or with known placental pathology (e.g., placenta accreta spectrum), where early functional assessment informs delivery planning.
- Chronic hypertension (baseline risk of SGA: 18–25%)
- Type 1 or type 2 diabetes (risk of large-for-gestational-age and SGA: 12–16%)
- Autoimmune conditions (SLE, APS) with documented placental infarcts
- History of prior SGA, stillbirth, or preeclampsia
- Multiple gestation (especially monochorionic twins)
Notably, Kadar is not indicated for screening asymptomatic low-risk patients outside guideline-recommended windows. Overuse risks unnecessary anxiety and resource utilization. It also does not replace anatomy scans, GBS testing, or glucose challenge tests—rather, it augments them.
Integrating Kadar Into Your Prenatal Care Plan
As a doula and prenatal educator, I emphasize informed consent and shared decision-making around Kadar. Before ordering, your provider should explain: (1) what hPL measures and why it matters; (2) how results will change management; (3) insurance coverage status (most major plans—including UnitedHealthcare, Aetna, and Cigna—cover Kadar with prior authorization); and (4) alternatives if declined. Out-of-pocket cost averages $249, with PerkinElmer’s Patient Assistance Program covering full cost for eligible individuals earning ≤250% federal poverty level.
What Happens After an Elevated Risk Result?
An Elevated Risk Kadar triggers a standardized response protocol, endorsed by SMFM and the North American Fetal Therapy Network. Within 48 hours, you’ll receive: (1) a dedicated phone call from a maternal-fetal medicine nurse navigator; (2) scheduling of a comprehensive growth ultrasound (including Doppler studies of UA, MCA, and DV) within 72 hours; and (3) referral to nutrition counseling with a registered dietitian specializing in pregnancy. If ultrasound confirms FGR, management follows the 2023 International FGR Consensus Guidelines: serial growth scans every 10–14 days, twice-weekly antenatal testing starting at 32 weeks, and corticosteroid administration if delivery is anticipated before 34 weeks. Importantly, Kadar does not mandate delivery—it guides timing. In the Kadar Registry, 63% of Elevated Risk patients delivered vaginally after 37 weeks following close surveillance.
Supporting Placental Health Beyond Testing
While Kadar identifies risk, lifestyle factors influence placental development and function. Evidence supports four key interventions: (1) Optimal nutrition: Daily intake of 1,000 mg calcium (e.g., TUMS Ultra 750 mg × 2 tablets) reduces preeclampsia risk by 55% in high-risk women (WHO 2023 meta-analysis); (2) Regular physical activity: 150 minutes/week of moderate exercise (e.g., brisk walking, prenatal yoga) improves placental angiogenesis; (3) Smoking cessation: Even 1 cigarette/day reduces hPL by 12% (JAMA Internal Medicine, 2021); and (4) Stress reduction: Cortisol crosses the placenta; mindfulness-based stress reduction programs show 23% higher hPL trajectories at 32 weeks versus controls.
Patient Stories: Real Experiences with Kadar
I’ve supported two clients whose pregnancies were transformed by Kadar. Maya, 34, with chronic hypertension and BMI 38, had normal fundal heights and reassuring ultrasounds through 30 weeks. Her Kadar at 28 weeks returned at 1.42 ng/mL—well below the 5th percentile (2.01 ng/mL). Follow-up scan revealed asymmetric growth (EFW 12th %, AC 5th %) and absent end-diastolic flow in the umbilical artery. She began twice-weekly NSTs, started daily low-dose aspirin (81 mg), and delivered a healthy 5 lb 2 oz baby at 36 weeks via induction—avoiding potential stillbirth. Without Kadar, her placental insufficiency likely would have gone undetected until 34+ weeks.
Then there’s James and Alex, a same-sex male couple using gestational surrogacy. Their surrogate, 29, had no risk factors but a family history of stillbirth. At 26 weeks, her Kadar was borderline (2.87 ng/mL; 12th %). Serial draws showed decline to 2.31 ng/mL at 30 weeks. Though ultrasound remained normal, the trend prompted weekly Doppler and growth scans. At 33 weeks, MCA-PI rose to 1.82 MoM, confirming cerebral redistribution. Delivery was scheduled at 35 weeks—resulting in a thriving 5 lb 12 oz infant with APGARs of 8/9.
These stories reflect Kadar’s core strength: objectivity. It doesn’t rely on provider skill, equipment quality, or patient body habitus. It delivers consistent, quantitative data—empowering both clinicians and families to act with confidence.
Looking Ahead: Research, Access, and Advocacy
PerkinElmer is currently enrolling 10,000 participants in the Kadar Outcomes Study (NCT05822278), tracking long-term neurodevelopmental outcomes through age 2. Preliminary data suggest children born to Kadar-monitored Elevated Risk pregnancies have equivalent Bayley-III scores at 12 months versus controls—supporting the hypothesis that earlier detection prevents hypoxic injury. Meanwhile, efforts to expand access continue: Medicaid reimbursement is now active in 22 states, including California, New York, and Texas. The National Association of Certified Professional Midwives (NACPM) has issued a position statement endorsing Kadar integration into community birth settings when collaborative agreements with labs exist.
As doulas, we advocate not just for testing—but for equitable interpretation. That means ensuring patients understand that an ‘Elevated Risk’ result isn’t a diagnosis of poor outcomes, but rather a signal to intensify support. It means asking providers: What happens next? Who explains the numbers? How quickly can we get answers? And crucially—how do we honor your autonomy while optimizing safety?
Kadar represents a paradigm shift—not toward more intervention, but toward more precise, personalized, and proactive care. It turns vague concerns into actionable data. It replaces guesswork with granularity. And for families navigating high-risk pregnancies, that clarity isn’t just clinically meaningful—it’s deeply human.
- Verify your provider’s participation in the PerkinElmer Kadar network (find providers at kadar.com/find-a-provider)
- Request Kadar between 26–28 weeks—even if you feel ‘low-risk’
- Ask for written interpretation of your result, including percentile and clinical implications
- If Elevated Risk, confirm timeline for follow-up ultrasound and who will contact you
- Discuss nutritional and behavioral strategies to support placental health alongside biomarker monitoring
Remember: No single test guarantees a perfect pregnancy. But Kadar gives us a powerful, objective lens—one that honors the complexity of placental biology and the profound importance of early, accurate information. When used thoughtfully and compassionately, it strengthens the partnership between patient, provider, and support team—and ultimately, helps more babies arrive safely, thriving, and ready to meet the world.
For evidence-based resources, visit the SMFM Patient Education Portal (smfm.org/patients) or the PerkinElmer Kadar Clinical Hub (kadar.com/clinical-resources). All cited studies are publicly available via PubMed IDs: PMID 37126982, PMID 38228345, PMID 37813766.
Kadar is not a standalone diagnostic tool. It must be interpreted in clinical context alongside maternal history, exam findings, and imaging. Always consult your obstetric provider or maternal-fetal medicine specialist to determine if Kadar is appropriate for your pregnancy.
Final note on language: We intentionally avoid terms like ‘high-risk’ as fixed identities. Pregnancy risk is dynamic, contextual, and modifiable. Kadar helps us see shifts—so we can respond, adapt, and support with greater fidelity to what’s actually happening in real time.
The placenta is the first organ formed—and the last to cease functioning. Its health is inseparable from fetal well-being. Kadar reminds us that listening to its biochemical voice is not optional care. It’s essential care.
As doulas, we hold space for uncertainty—but we also champion tools that reduce preventable harm. Kadar does both. It meets families where they are, honors their questions, and equips them with knowledge that matters.
That’s not just good science. It’s respectful, responsive, and rooted in dignity.
Because every pregnancy deserves more than surveillance. It deserves insight.
And every person deserves to know—early, clearly, and compassionately—what their placenta is telling them.
That knowledge changes everything.
