dissenting.
Notwithstanding the majority’s extension of the increased-risk test, plaintiffs’ case founders on the failure of their expert, Dr. *392Kalafer, to offer anything more than a net opinion in support of their claim against defendant, Dr. Pawliw.
Generally, plaintiffs must present expert testimony to support the causal connection between a doctor’s alleged malpractice and a claimed harm. Germann v. Matriss, 55 N.J. 193, 205, 260 A.2d 825 (1970); Lanzet v. Greenberg, 126 N.J. 168, 193, 594 A.2d 1309 (1991) (Pollock, J. dissenting). Without an adequate factual basis, the expert’s testimony fails as an impermissible “net opinion.” Nesmith v. Walsh Trucking Co., 123 N.J. 547, 549, 589 A.2d 596 (1991). “The ‘net opinion’ rule appears to be a mere restatement of the established rule that an expert’s bare conclusions, unsupported by factual evidence, [are] inadmissible.” Buckelew v. Grossbard, 87 N.J. 512, 524, 435 A.2d 1150 (1981); Lanzet, supra, 126 N.J. at 186, 594 A.2d 1309; Nesmith, supra, 123 N.J. at 549, 589 A.2d 596. The rule, moreover, often focuses “on the failure of the expert to explain a causal connection between the act or incident complained of and the injury or damage allegedly resulting therefrom.” Buckelew, supra, 87 N.J. at 524, 435 A.2d 1150. An expert opinion “must be based ‘primarily on facts, data or other expert opinion established at the trial.’” Id. at 525, 435 A.2d 1150 (quoting Evidence Rule 56(2), now embodied in N.J.R.E. 703).
In his videotaped deposition introduced at trial, Dr. Kalafer concluded that the failure to perform a biophysical profile (“BPP”) and nonstress test (“NST”) on December 21 increased the risk that the fetus would die:
If a study would have been performed such as the nonstress test and biophysical profile, one could utilize that information; and if it was abnormal, the baby could have been delivered most likely in a setting more appropriately, and the baby could most likely live in the outside world.
[I]f these studies were performed, it would have helped the doctor to continue the in útero life or basically either decide this baby does not have to be delivered or just continue close monitoring.
*393When asked whether to a reasonable degree of medical probability the tests would have revealed the effects of placental and umbilical cord abnormalities, Dr. Kalafer testified that:
I feel that if a study would have been performed, one could utilize that knowledge to help better manage the pregnancy. If the test would have been normal, it would have been reassuring. If the test would have been abnormal, then I believe one would have been pushed to deliver this baby.
Both the Law Division and the Appellate Division found that Dr. Kalafer’s testimony was insufficient to establish that Dr. Pawliw’s asserted negligence had caused the death of the fetus. Specifically, the Appellate Division reasoned that:
Although Dr. Kalafer indicated that a nonstress test and biophysical profile would reveal fetal stress, he did not express an opinion that the fetus was in fact in stress on December 21, 1988. Consequently, Dr. Kalafer was unable to state “within a reasonable degree of medical probability” that either test would have produced positive results that could have led to the early delivery of the baby— Dr. Kalafer’s [testimony] constituted a bare conclusion, unsupported by any opinion as to the critical underlying fact of the fetus’s condition as of December 21, 1988.
[285 N.J.Super. 113, 122, 666 A.2d 592 (1995).]
The majority disagrees, taking comfort in measuring Dr. Kalafer’s testimony against a lower standard of causation, the increased-risk standard. Ante at 390-391, 696 A.2d at 616-617. According to the majority:
Sufficient factual evidence was presented by Dr. Kalafer to the effect that if the tests had been performed a stressed in útero environment might have been observed. Dr. Kalafer testified that the placental and umbilical cord abnormalities noted in the autopsy report were consistent with the patient’s complaint about the decrease in fetal movement. He stated that “it might have been indicative of the fact that this placenta was not nourishing the baby appropriately,” resulting in stress to the fetus. Dr. Kalafer stated that the NST and BPP tests might have detected a “smoldering” uterine environment, which would have indicated either the need for continued closer monitoring by the obstetrician or an early induction of labor.
[Ante at 390-391, 696 A.2d at 616-617.]
Dr. Kalafer’s testimony does not provide an adequate factual basis to support his conclusion that the failure to conduct the BPP and NST tests on December 21 increased the risk that the fetus would die. Vague statements about “manag[ing] the pregnancy” and a “smoldering” uterine environment cannot save a net opinion.
*394The omissions in Dr. Kalafer’s testimony are as telling as his actual testimony. Dr. Kalafer did not testify that either the ultrasound conducted on December 27 or the autopsy report supported his conclusion that the failure to perform tests on December 21 increased the risk that the fetus would die. Although the autopsy revealed umbilical cord and placental abnormalities, Dr. Kalafer did not say that those abnormalities indicated that the fetus was in stress on December 21. Indeed, Dr. Kalafer admitted that he could not state to a reasonable degree of certainty that the tests, if performed on December 21, would have shown the fetus was in stress.
In contrast, Dr. Wilchins, defendant’s expert, discussed medical evidence to support his conclusion that the failure to perform the tests on December 21 did not increase the risk. For example, Dr. Wilchins stated that the ultrasound on December 27 revealed “two very large amniotic fluid pockets of adequate measurement— That indicates that the fetus had to be functional within 24 to 48 hours of the [ultrasound].” He further testified, “fy]ou could not have had a compromised fetus on the 21st and have had normal amniotic fluid on the 27th,” because the fluid levels are maintained by the fetus urinating. Discussing the autopsy report, Dr. Wil-chins stated that the “faint meconium staining” demonstrated that the fetus was not in stress on December 21. He noted that staining is the result of an “in útero fetal bowel movement,” which occurs when the fetus is “very stressed.” Dr. Wilchins opined that if the fetus had been in stress on December 21, then “both the fetus and placenta [would] be green.” Here, however, there was only faint staining. He concluded:
[T]hat in turn ties in with the pathologic estimate of [a] couple of days of fetal expiration, which in turn ties in with the normal amniotic fluid volume. So putting these ... pieces together, and then going back to the 21st, one can see that you could not have had fetal distress at that time and yet turn up with these objective findings.
Although sympathetic to plaintiffs’ loss, I would affirm the dismissal of their complaint. Even under the increased-risk test, plaintiffs failed to prove their case. Changing a legal standard *395does not provide a factual basis that can salvage a net opinion. Without an adequate factual basis, the majority opinion remains an artistically designed castle in the air.
I would affirm the judgment of the Appellate Division.
For reversal and remandment — Chief Justice PORITZ, and Justices HANDLER, O’HERN, GARIBALDI, STEIN and COLEMAN — 6.For affirmance — Justice POLLOCK — 1.